I found condoms, pics & voiceml msgs from grls.we have a 2 mth old.I want 2 be w/him,but its hard 2 trust him?

He admits to giving girls his number in the past, but he swears it never went further than that, but the messages I've heard and the pictures I've seen indicate something different. One girl even called me and told me they had . Since we've had our child two months ago, he's hasn't been going out as much and he has apologized for giving his number out and says that he wants us to get married but I'm afraid to trust him again. Deep down inside I feel like I should leave him, but we have a child together now and I want my child to grow up with a stable family environment. Another part of me wants to give him a second chance, but I feel like if I just "forgive" him this easily he'll do it again..and maybe more the next time. What should I do? Should I give him another chance or should I just let it go? We've been together for 3 years now.