Help!!

(No judgement please!) but im a little confused, i recently just found out im pregnant, (5 weeks 5 days according to my lmp) i had broken up with my now bf for like 8 mths (we were having issues and decided on a break) and i had intercourse with someone else on the 5th of may with condom and he never even got to finish...got back with my bf on the 20th of may and we were having unprotected sex every single day a couple times a day even...my first day of my last menstrual period was around may 18 so its safe to say its his right? Not the one i had intercourse with once and protection and never finished