First off, how did you "find" that picture? Was it really just lying around or were you snooping? If you were snooping, why? You already know he's still with her. I've worried about you in the past but now I worry about you and your baby.
Look, if he is going to continue to treat you like sh*t, he's got the potential to start treating her like sh*t too. Eventually he's going to treat the OW like sh*t but who cares about that, that's not your problem.
Michelle, you need to separate yourself and your daughter from him. Period. If he comes back with the "I want to make this work...I'm sorry...she's out of my life" crap, don't fall for it. Talk to your parents, talk to a counselor, get help somewhere, somehow. You are potentially in a cycle that is never ending.
Break the cycle. Break the cycle. Please someone, back me up on this.