Am I being unreasonable to ask my bf to choose between his girl bsf and me?

Is it bad to ask my bf to choose between his girl bsf and me?Me and my bf have been together a year and a half and met at University. Since I have known him he has had a girl bsf lets call her ‘vicky’. Vicky and him met 4 years ago in the club, they made out with eachother and went on a couple dates before they decided they weren’t interested and instead became ‘friends’. I have met her a once or twice, the first time at my bf’s birthday. She was the first one to arrive and all my bfs attention went to her. They sat on the sofa pretty much the whole night, knees touching in deep convo, even when it was time to move on to the club he wanted to stay with her chatting instead of going, he told me to go off with my friends and have a good time. Of course I was really hurt. Btw, I ‘dragged’ him out to the club since all his friends came that night for him, not to go without him. Fast forward, Vicky and my bf would meet up every month for a ‘catch up’, she lived alone and he would go around hers and she would cook for him and they’d watch a movie together. I became really uncomfortable with this and told him I dont like him going over to her flat alone and to only meet in public. He agreed and that was that. Presently, around a year later, they still talk every week and he has moved away to a different city so they havent met up for a while. I have been feeling quite anxious and jealous about their relationship, I felt like there was more then meets the eye. I asked to him if I can read through their chats, he was a bit hesitant but put me on snapchat and handed me the phone. There was nothing there as most of it was unsaved. I asked to look through his text messages, he told me what I was about to see was mostly old stuff and im not gonna like it. What I saw just broke me. There was nothing presently texted to eachother, but the texts before were completely inappropriate. The SAME week my bf asked me to be his gf she texted him ‘hello my favourite man in the world, how are you?? I miss you so much and i would be so lost without you’ she would also in depth talk about her sex life to my bf, telling him every little detail, she would text him continuously saying she loved him and he would say it back. They would call every night on the phone for hours and they would flirt back and forth in their messages.after reading all that I felt sick and was shaking. I know there was no evidence of this chat AFTER we got together but there was definitely some sexual chemistry going on right before he asked me out. I broke down and cried, i told him the whole thing makes me incredibly anxious and I dont feel comfortable him and vicky being friends anymore, especially since she is constantly texting him to meet up. he told me hes not going to stop being friends with her because what if she did something to herself and he wasnt there for he (she has mental trauma from the little i know). I didnt know what to say as I personally dont feel their relationship is appropriate, I asked him if he had feelings for her and he denied it. I ended up saying its either her or me, too which he said I cant control him, which is true, but this anxiety is killing me. i dont feel special to him anymore, I feel second best.He ended up saying to me he wont meet her unless in a group and he’ll have to say the reason is because I dont like their relationship. But that just makes me feel like b***. Am I being reasonable here?