Ok.. relationships...?

okay well, my bestfriend same age as me had a baby yesterday. and she is saying thay my boyfriend is the father to her child. my boyfriend and i have been together for 2 years and obviously a pregnancy lasts 9 months. adam told me he hadnt slept with jess since they broke up 2 years ago. and i dont know who i should believe. him whos telling me that he hasnt slept with jess or jess whos telling me its adams baby.. in a way i think jess still likes adam and is jealous of me and him so is trying to get us to split up. but adam has been a bit quiet when i talk to him about it. so i really dont know who to beleive... opinions? x