Boyfriend still friends with former lovers

Dear all,

I am quite confused and I am looking forward to your insight into my situation

I have been in a relationship for a year now (we do live far apart but see each other quite often). My boyfriend hasn`t been in a relationship for quite a while and (possibly) as a result of that, he had a few sexual relationships with some of his female friends.

I know of two, which he is still friends with and very much hanging out with (we are talking about seeing each other every week, more than me and him see each other).

4 months after we met, he went to Japan on a trip with one of these girls (about three weeks). It was terrible for me. The reason was/is (and I do really how that you can help me out here) NOT because I actually feared that something would happen between them.
It just feels so inappropriate.

I have met one of these girls. While she was very nice to me, it also felt like she felt entitled to him in a weird kind of way. After a few meetings, I told my boyfriend that I don`t want to meet her anymore.

He claims that with one of those girls, it is just a very close friendship that he values. So apparently they had been friends for a while and then felt that there is something more. They had sex a couple of times and decided that there wasn´t any attraction. That is what he told me. SInce then, they went back to being just friends. She has a boyfriend now and when we meet, it just doesn´t feel like my boyfriend is paying attention to my feelings at all. It does happen that him and his ex are walking in front of me while he has his arm around her.

My problem is that whatever I do or say, I am fighting a losing battle. I am not a jealous person, nor did I ever encounter this problem in a relationship.
If I decide to just "go with the flow" and accept it, I feel terrible.

If I´d tell him that I am not comfortable with him seeing her, I would break up a friendship and he will hold it against me. And quite frankly, I am not sure that he would even "choose" me.

While everything else is great between us and I love him and think we are a great couple, this situation is really keeping me from committing fully to him.

Please give me your advice. I am really out of ideas.