Girlfrienemy

Super hot girlfriend that's out to stab your back but for some reason keeps on kissing you and telling you she will never leave.

Names chosen randomly

Mark: My girlfriend just cheated on me.
Dave: That sucks. With who?
Mark: With my cousin.
Dave: Why? She hates your cousin!
Mark: She was pushing for that new job downtown in the corner office for me.
Dave: What's the problem then?
Mark: She's interested in the man my boss will be.
Dave: She's a real Girlfrienemy isn't she Mark?