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3.
The boy that you have sex with and do all the other relationship type things with. You are probably invited to all of his family functions yet you are introduced as just a friend. You may even live together or have children. He refuses to commit and maintains the attitude that having a "Relationship" will ruin your friendship. He may even date other women and you are expected to think nothing of it. "Un" Stemming from "Alice in wonderland's" Un-birthday. Where it's not your birthday but you celebrate like it is.
Un-boyfriend: Hey Stephanie you wanna come back to my place?
Stephanie: Aren't you living with Amber?
Un-boyfriend: Well yeah but we just share a bed we're not in a "relationship".
by fairybitz August 11, 2008
 
1.
A boy, who a girl considers to be boyfriend material of showing interest but is otherwise unwilling to commit or admit feelings for said girl. Both may hang out and do boyfriend/girlfriend things, but not go steady.
Zach was Amanda's unboyfriend. They both always did things with eachother and Zach felt comfortible enough around Amanda to share his feelings with her. Just not his feelings for her.
by Jennifer February 21, 2006
 
2.
A man with whom you share an amazing emotional bond and yet he is not your boyfriend.
My unboyfriend called today. We talked about everything except his girlfriend.
by Ms.Little February 18, 2010
 
4.
The guy a woman hangs out with and does boyfriend-girlfriend relationship things with, but she's not really going out with him nor does she want to sleep with him.
friend: What did you do last night?

woman: My unboyfriend and I went for a nice dinner.

friend: Did anything happen between you two yet?

woman: No, we're just friends who happen to be undating.
by bambolii April 19, 2012