What should I do? stay n deal with it or get out now!?

So I've been with my bf for 14 mo. we have had a pretty good relationship except for one problem, he has this girl "friend" who he says repeatedly they are just friends and they will never b anything more, this he knows for a fact. Well about 9 mo. ago he finally came out n admitted that he has feelings for her they have been friends for 10 yrs n shes also married with children, well her husband ped away n that's when he admitted this. I already knew he did b/c the way he would always talk to he n about her, he would also buy her Christmas n birthday gifts while none of his other friends even get so much as a card! (i know im stupid!) they would go out weekly to lunch or breakfast and occasionally to concerts he was always payin her way! Anyways after he told me about his feelings for her they stopped talking, texting, n hanging out. but now lucky for me shes in the picture again I've told him how i felt that i feel uncomfortable with him hanging out with her n he ures me that there wont b anything happening cause they have talked about it b4 n decided they were 2 good of friends n didn't want to ruin that. plus hes with me n he loves me, blah blah blah, however not enough consolation for me. basically hes told me hes not giving her up so i c it as either deal with it and feel miserable about the whole thing n continue u fighting weekly when they decide to go out-or leave. if i could just have someone else's opinion on what they would do? ya know a different perspective! I am also 4 mo. pregnant by him!!