How do you know if hes being completly honest with you?

My boyfriend has cheated on me once before with his ex girlfriend but we have grown together and got past that point in our relationship and I have just gotten my trust back for him. I used to go through his phone all the time because I always had this feeling he was talking to girls or his exs. So after 3 weeks of seeing that he hasnt talked to any girls... three weeks later this morning I decided why not check up on him to see if hes still being committed to me. Well 2 months ago he was talking to this girl devin well I deleted her contact from his phone but then she texted him again i suppose and I found this morning hes talking to some girl whos contact says D. Well he asked her if shes still pregnant so that gives me a gut feeling he did meet up with her and supposably got her pregnant. this is what happend.... Hey whats up >> from D Nothing so you still pregnant? >> HIM yes but it will be all taken care of saturday. >> D So wouldnt you think HEY HE CHEATED ON ME AND GOT A GIRL PREGNANT???? CAN SOMEONE PLEASE HELP ME!!! I DONT WANT TO LEAVE HIM but im coming to see that I just might have to. This is the man i truly care the most about and love so much but iv comed to the point where idk what to do!!! PLEASE HELP SERIOUS ANSWERS ONLY!!! THANX.