Pregnancy Timeline & Paternity: Estimating Conception & Fatherhood

Question
When did I get pregnant I had my last period may20 had sex all wit my boyfriend till july 15 wit another guy my due date feb20 who's the dad

Answer
Based on your last period, it looks like you conceived around June 3, give or take a few days. Whoever you were having sex with between June 1 and June 10 is the father.  

If the only date you had sex with the other guy was July 15, then he is definitely not the father.