See Article: Relationship with Kai Green
See Article: Relationship with Julie Yamamoto
When Ester first met Ben in Hot Stretch, they fought for the fusion device. Later when she realized her kind was doing evil things, she joins Ben's team. She brought him to her friends' town and they played an alien version of hockey. Ben turned into Water Hazard and splashed everyone with water to cool them down, even when Ester told him not to. He then brought her a towel, and she blushed as he gazed at her. She turned the water floating around him into snowflakes and ran off laughing. Rook told Ben she liked him. Later when she became the chief, she hugged Ben and told him she and her kind would be good neighbors. Later Ester's friends called Ben her boyfriend, and Ben at first denied it, but then excitedly asked Rook if he had a chance with her.
In Rules of Engagement, Ben offered to help clean up the Hot Spot with her. She excitedly agreed, wrapping her arms around his arm. She also stated that she is fond of Mr. Smoothy.
Sometime before Return to Forever, they went on a movie date.
In Fight at the Museum, Ester invited Ben to the museum for a date, but Ben, not knowing it was a date, brought Rook since Rook enjoys museums. Ester is shown to be horrified when she hears that Ben and Kai end up together in the future Spanner comes from, while Ben himself states there's no way that's going to happen.
Later in The Most Dangerous Game Show, feeling that Ben really was destined to be with Kai, Ester decided to let go of him. While trying to talk to Ben, who she couldn't get in contact with, Ester ultimately fell in love with Antonio. Eventually, Ester made her feelings known to Ben, breaking up on good terms, even stating she still likes him while remaining friends.
In Many Happy Returns, when Kevin was about to marry her, Ben challenges Looma to a battle to stop it. She keeps defeating him until he turns into Four Arms. When Four Arms defeats her, it is revealed that female Tetramands marry the ones that defeat them in battle. Kevin and Gwen leave, and Looma says she'll be back in three years. Ben mutters that Kevin is "so dead".
In Rules of Engagement, Looma returns, attempting to collect four items for their wedding: something conquered, something bruised, something severed, and something blue. Looma battled the Kraaho, the tribe of Ester, to capture one of them as something conquered, and Ester asked Ben for help. Looma was happy to see Ben again, but was busy with collecting the items. Ben tried to stop her, but she tossed him aside and took Ester, Rook, Julie, and even Hervé, for being a photographer. She also captured Fistina's right hand, which leads Fistina and Ben to get it and "little Rook" back. Looma went to Ben's house and was happy to see her future "mother-in-law" and presented her "offering gifts". When the "offering gifts" tried to escape, Looma tried to re-capture them. Looma fought Julie when she heard that she is Ben's girlfriend, not knowing that they broke up. With the help of her friends, Julie was able to defeat Looma. Looma was saddened, but accepted her defeat. However, Looma promised Julie to crush her skull the next time her and Julie meet again.
In The Frogs of War: Part 2, Bullfrag infiltrates her team and from the moment she saw him, Attea had a crush on him. When they meet in the cell block of Plumbers HQ, Bullfrag comes up to her and starts flirting, taking note that his new form shows her in a whole new light. Attea is a bit flustered, but starts flirting back, only to be knocked out by a mana blast by Gwen. Bullfrag says that happened because he was being influenced by the Incursean DNA.
At the end of the episode when leaving Earth, she gives Ben the offer to come with her and "Ditch that monkey face and turn into Bullfrag again" He promptly declines. Attea gives him a frog-like kiss to the back of his head with her long tongue, winks, and takes off.
She later decides that Ben is her only option for a mate in Catfight, however Ben later convinces her that she is capable of ruling on her own.
Elena Validus is one of the Plumbers' kids and a former member of Ben's soccer team. She is mentioned by Gwen as Ben's first crush, though this contradicts what was seen in the original series, as Ben met Elena when he was thirteen, while he met Kai when he was ten, but Kai never actually liked Ben. Rook also says his first crush was Patty Berkenfeld. Ben had to convince his soccer teammates to let her join. She appeared in the live-action film Ben 10: Alien Swarm.
Elena also appeared in Revenge of the Swarm, where she served as the Queen of the Hive. Victor Validus was attacking Ben at night, so the trio went to her to find whether she knew anything about the Nanochips. Later, when Ben mentioned Julie, it made her angry and jealous, and kidnapped her in order to keep Ben all to herself. They almost kissed, but her plan was revealed to Ben and he saved Julie. Elena, being possessed by the Hive Queen, encountered Armodrillo and choked him with the nanochips. However, she was convinced by Julie to not to do so if she had really liked Ben, and the true Elena, that still cared for Ben, willingly sacrificed herself in order save Ben, proving how much she liked him and that there was still the Elena that cared for him. Ben became sorry for her, understanding how much she had liked him. At the end of the episode, the nanochips reform, revealing she is still alive.
Elena appeared in The Perfect Girlfriend disguised as Julie. As Julie, she tried to do everything to make Ben happy. Once Ben finds out Julie is Elena, he tried to reason with her and fought her as Ultimate Echo Echo, but lost after she choked him with Nanochips again. Julie tells Elena that if she kills him, then no one can have him. At the end of the episode, Elena retreats into the sewer, "knowing what hate feels like" and promises to return.
Jennifer Nocturne is a famous film actress who appeared in Hero Time, when she had an instant crush on Ben when he saved her, then kisses him from the lips in public. Later, she tried to make up a relationship with Ben for publicity and to make a better career for herself. Later on, she was captured along with Julie by Captain Nemesis, who later called himself Overlord. When Overlord had the two of them hanging from a statue, he gave Ben the option to save one of them before blasting the cord holding them. Without any hesitation, Goop saved Julie while Kevin and Gwen saved Jennifer.
Ben and Kevin started flirting with Eunice and she stated that Ben was bad at flirting. In the end, Ben let her go because she is the Unitrix and quite possibly dangerous, and also due to having Gwen's randomized DNA which makes her technically related to him. Azmuth, at Ben's insistence, decided to compromise and have her be Azmuth's assistant. Before Eunice leaves with Azmuth, she gives Ben a blue flower as a reminder of her. In Simian Says, Eunice kissed Ben on the cheek.
In T.G.I.S., Ben gains a crush on Drew Saturday the minute he saw her. When Doc tells Ben, Rook, Zak, and Fisk that Dr. Animo and his Chupacabra army are attacking Mr. Baumann's store, Drew offers to stay behind to look after the petrified alien. Ben though suggests that Rook stay behind and Drew come with him, telling them that they might need her medical expertise. Later, when Ben, Rook, Zak, and Fisk arrive at the airship to stop V.V. Argost and his army of cryptids, Doc and Drew reveal themselves and tell them that they escaped moments before Argost showed up. Ben then instantly tells Drew that he's happy that she's okay, causing Zak to tell him that Doc is okay too. At the end of the episode, Ben tells Zak how it was a pleasure to work with him and his mom. He then takes a photo with Zak, Doc, Drew, and Fisk as Four Arms.
Drew knows about his crush and finds it cute and amusing, but Zak doesn't appreciate his crush, but still remains his friend.
Emily briefly dated Ben, but the reason they broke up was that Ben went "hero" and left Emily on a 200 foot tall watchtower, causing Emily to hate Ben.