Background
I have a friend for almost three years now, we are both 24 y.o, we have always been so close and, even if we live far away from each other (+9000km), we have spoken every single day since we parted ways.
I have been to his country (in South America) to visit him in 2017, and he has recently come to mine to visit me (Europe).
Since the beginning we have liked each other, but distance and me being in a relation ship - with a guy I really love - made it impossible to have a romantic relationship. However, it's true that when we saw each other, we were behaving more like a couple than just friends: cuddling, spooning, holding hands…
I went to visit him in 2017, and after a month, he met a girl with whom he started a friends with benefits relationship and eventually ended up being her boyfriend. At that time, my friend and I were planning a trip of one month together, and his girlfriend got jealous.
During that time, she was getting jealous every time I was sending messages to my friend to the point that he had to show her the messages we were sending each other in Instagram, and he would stop talking to me if she was around, which seemed unfair to me, and I told it to him.
During the trip I asked my friend about his feelings towards me and his girlfriend, and he told me he likes me more and he enjoys talking with me more. He also said he didn't want to be in an exclusive relationship with his actual girlfriend.
Now, after the trip, he talked with the girl and told her that he had cheated on her several times and that he didn't see her as girlfriend, so they stayed as friends, which is cool if they feel like being friends.
The problem
The problem came when now, after the trip and the break up, they met again (as friends), and he went to sleep at her house, and he stopped answering my messages.
That would be ok if he does so because he really wants to. I mean, I don't want him to feel forced to answer me, and I would be perfectly fine with it if it were his own choice. I have asked him before if he doesn't reply to me because he doesn't want or just to not make the girl feel jealous, and he always said the second scenario.
This is where I mainly see the problem. Because somehow he's being manipulated, not directly though, to stop talking to me or not talking that much, while he has the will to do it. And I believe him when he says so, because as soon as he leaves the girl's house he replies to all my messages saying "Sorry, I was with the girl etc".
What I want
What I want to achieve is to make him realize that his relationship with this girl is affecting our relationship. And that theirs is not a healthy relationship as she has checked messages I have sent my friend and he's stopped doing things we both like (talking to each other) just to avoid his ex being jealous again.
I am searching for advice as I want to say it in a way that I don't sound jealous of them being together again (as friends or whatever), as I am really not.
I just want him to open his eyes and realize that it's not a healthy relationship. I am aware that talking about such a sensitive topic might make him feel like I am jealous and that I'm trying to get him to avoid interacting with her. As I said, we like each other, and I would like to handle the problem without making him feel this way.
What I've tried so far
Before the trip, when he started doing the same, I talked with him very seriously and I told him that this kind of behavior annoyed me, because he was not talking to me just because she was feeling jealous/bad.
When I told him about it, I also talked about his relationship with her and he realised he needed to tell her that he was not seeing her as a girlfriend and so on, he waited to come back from the trip and he said it.
He also stopped doing like that and he was talking to me while going to the toilet or so if he was in the girl's house or the girl was around him.
Now, I am surprised he did it again as I already explained him how I was feeling about it before (in July) and he seemed to understand it.
Question?
How could I approach him with the topic again so he can understand my feelings and that he is not in a healthy relationship?
Additional information
I don't want a relationship with my friend as I am more than good with my actual boyfriend.