Should i believe him n get over it or not:/

I'm 16 and my boyfriend is 19 he has a daughter already that is 1 yr and 4 months and he's not with his babymomma anymore obviously but I don't know I have a feeling he still has feelings for her or something they been together for 5yrs and me n him just got together like last month. I looked thru his msgs n I found the ones with his babymomma and 5 days before we got together officially they were talking about how much they miss each other and how they wanted to have sex again and he kept saying he still loved her. Thats too recent to when we got together. I don't know what to believe. He says he doesn't have feelings for her anymore & that all his feelings are all into me. I want to believe him but being with sumone for 5yrs I think he still does.. & I'm pregnant..he knows already he said he did it on purpose he kept telling me he wants me to be his baby's mother n hes going to get our zodiac sign tatted on him with our date on it(were the same sign). I really do like him I'm slowly falling for him I just don't want to look dumb. I don't wana be lied to. I don't want to be with someone that still has feelings for their ex:/ he keeps denying it but the msgs say something different. I don't know if he was just trying to use her for sex or what (btw she has a bf n was cheating on him with my bf but that was way before me & him got together)should I just believe him & get over it or leave idk what to do:/