I just feel unhappy about it!!

So been dating this guy for few months. He is sweet, kind and we get along pretty well. But his best friend is a girl and she happens to be ex girlfriend of his NOT so longer friend . Its making me uncomfortable for my new bf to have another woman as a best friend. When I tried to express my feelings about it, he became very defensive and seemed more protective of their friendship/relationship then the one we have and we ended up in a fight which has left me with doubts. He has also told me that he confides in her about our relationship. I am ready to let him go as to be honest I have warranted trust issues as it is but he is begging me to trust him and the relationship he has with the other woman. He is good to me otherwise and I think he is a good person but I have been in a terrible abusive, lying and cheating relationship in the past which has taken me two years to get over and find my happy self again. Finally I am ready to have someone in my life again and over the pain my last relationship caused me but for some reason I don't trust this relationship .I feel emotionally conflicted and blame myself of maybe being paranoid, insecure and not being fair to him and his woman best friend but then another side of me is terrified to being stuck in unhappy relationship again and my gut is saying this relationship won't work based on knowing myself and what I can handle and tolerate. I have promised myself to never be in another bad/ unhappy relationship again. I was single for two years before I met him. He is now saying he will gladly end that friendship to show how much he loves me but then that would makes me feel like shit and I am sure he will have a resentment towards me about it.. He wants me to meet and get to know the girl first and if I still feel the same way then he will end their friendship. Has anyone ever had these feelings/dellema/situation i am having now? If so how did you handle it or solved it? I am Open to advice and truth.