Boyfriend Holiday with female he slept with

mishelE

My boyfriend and I are in a great relationship. we've been together for almost 2 years and the more time we spend together the better we get on and we are seriously considering moving in together soon and are quite positive about it. when we do argue is when it comes to other girls. He has admitted to having a wandering eye, (not hand though) and I do trust that he would not actually physically do anything but here's the deal:

There's this female friend he has been friends with since high school. He goes on a trip every year with her and 2 other friends (2 guys 2 girls in total). He has told me that he had feelings for her in the past or a while and they ended up sleeping together a couple of years ago. They remained friends after and last year he went on the same trip and he hadn't;t even told me there had been sth in the past between them. about 5 months ago they were going to meet just the two of them because he said he wanted to get "closer" to her again which I honestly hated. He has other female and male friends and I am more than happyy for him to spend time with them eat but this girl really bothers me.

It bothered me 5 months ago when they did end up meeting up, but I did tell him that it hurt me and he hasn't seen her since then. I did suggest maybe me meeting her would be an option to solve this. he agreed but I still haven't met her. Last time they were going to meet just the two of them he told me everything that had happened in the past and also that she is single and he is not sure what her intentions are because as he says she had been acting "strangely". He did try to adjust to he situation by not having seen her since then, but he just told me about this trip and I have been really hurt. I fell very uneasy because she ticks all his boxes and although I don't think he would actually physically do anything it's ****ty for me, there's just this huge knot in my stomach.

They are going as 4 people in total so I am wondering why he hasn't considered maybe asking me to join? I really like him otherwise, we are great at communicating ect and we want to be together but it is hurting me a lot and  I don't know hoe to solve this situation. when he told me we were on our way home and I kind of ignored him, I needed time to think (because I was quite hurt) and right now I don't really feel like talking to him / seeing him. how can we solve this? He sees it's hurting me a lot.