Easy
(2003)

Product namer and self described "jerk magnet" Jamie Harris (Marguerite Moreau) tries to make a relationship with an old English professor John (Naveen Andrews) but he goes back to an old girlfriend.  Meeting genuinely nice guy Mick (Brian F. O'Byrne), Jamie strives to change her way and start something real with him.

However, due to misunderstanding brought on by Jamie's paranoia, Jamie believes Mick is getting back together with his ex-wife even though he is only going to be a sperm donor.  Jamie has sex with another guy and Mick finds out; he angrily confronts her over her foolishness making it clear that her unhappiness with men is mostly of her own making. To make the night worse, she finds her sister in bed with John.

Several months later, at a party to celebrate's his ex-wife's child, Jamie reconnects with Mick and apologizes for how she acted. They decide to give it another try.

Thanks Spectre!