Some dude called my cell phone looking for my fiance

[DrewDevil]

All kidding aside, why is everyone bashing the OP?

He just found out his fiancee and mother of his child is banging someone else in a most terrible way.

Who among us WOULDN'T demand to know who it was and get angry enough to kick something?

He didn't hit his fiancee, he didn't destroy anything, and he didn't say anything that's going to end up in court one day.

OP: you did a good job managing your anger. Next step, talk to a family lawyer about custody between unmarried parents in your state.

Close all accounts and credit cards you hold jointly with your fiancee.

You don't necessarily have to move out.

Don't do or say anything you don't want repeated in front of a judge. Keep your cool.