Someone that you were in a relationship with but it wasn't quite a relationship. It could have been that:
1) You acted like you were in a relationship, except for lacking the physical.
2) You had the physical aspects of a relationship but outside of the bedroom you were just friends.
3) Almost a relationship except that one of you were in an actual full-blown relationship at the time, and the two of you couldn't quite get over that fact.
We had been sleeping together for three months and hung out together all the time but something was missing when were out on the town. I realized what was missing when we bumped into his boyfriend, which I guess made me his fauxfriend.