I have been with my boyfriend five years im 22 he is 30 i accuse him alot and nag him alot its like a disease?

i cant stop he takes care of home he does for my little girl and she is not his we have one on the way though and it will be his first child. My problem is that i found a condom in his coat pockett three years ago he said he didnt use them i found it again this year once and last year once i know he cud be lien but he swears me down he does not cheat. I wanna believe him and give him the benefit of the doubt. Should i forgive him....this man does anything for me and my child and now im carrying his first child do you all think he can change if he is cheating. I really cant say he is doing anything he is always with me and is in the house early everynight now since he found out im pregnant. were having a girl. How can we make this work? He does not seem to wanna be with anybody else he says he wants to get married and b a family idk what to do but i know i should stop nagging him so much being that he brings in the bread