Emotional cheating and backstabbing

To make a long story short, two of my boyfriends friends, including his best friend (whom I thought were my friends too) surprised me after a joint trip by telling me how much they disliked our relationship and that I was bad for him and a lot about how bad a person I was. And I can see that they have been thinking about this and based it on how I was in the beginning of our relationship, because I wasn't so into to my boyfriend and thus did not always treat him that well. But that was 3 years ago, and now this comes. Even worse, they didn't try to give me any constructive feedback, it was just a lot of condescending and mean accusations towards me such as "dont ask about feedback, it doesn't matter what we say, you can't convince us that you are good for him". Plainly, they had made up their mind. Then I tried to speak to his best friend because he really wanted us to be OK so I did it for him, but all I got was "you're not anyone we care about, you are just his plus 1".

So I was very hurt but each time I tried to speak to him he just said "I have to understand where they come from", and that he was protecting me and telling them to back off, that it was none of their business.

After repeated arguments over a few weeks we decided that he would not contact them for a month, so he could give me some time to just heal and not think about it. I thought 1 month was little but it seemed like a huge sacrifice for him so we agreed.

Today, less than a month after his promise, he accidentally conveyed that he had spoken to one of them, behind my back, but before the agreement. That came out only as i mentioned how wrongly i felt that they had behaved, and he said "well you didnt behave that well either, she told me" and that "i had to go behind your back because you wouldnt have listened"..! Are you fucking kidding me!? He assumes things do that justifies him betraying me?? Anyway, then I ask him when, and well, he had deleted his phone records. And when I say I can't commit to you when I feel like you are hiding things, could I please see your messages then? He freaked out, but soon understood that OK, I asked nicely instead of going behind his back like he did, and that he had caused my lack of trust. So I did and what do I find, he had continuously spoken to the very same people throughout this period, but behind my back, turning their notifications off. And when I confront him he just gives a load of bullshit like "I just answered " (he asked them 20 questions in like two weeks...) and that "not one month to the end of this month" (though he had written to his best friend throughout the period) and then again accusing me for "well you wouldn't have listened if I tried to talk with you about this" - when he hasn't brought up this problem to me. It's like if I were fucking someone else behind his back and saying well "you wouldn't have been happy if I came with the idea that I need to sleep with someone else because our sex life sucks".

I just feel so betrayed emotionally, his friends might have put the seed (unjustly, because whatever problems we have had in our relationship, it takes two to tango..), but he took the lead by actually betraying me and making us come apart.

I am also incredibly confused as to what I am supposed to do, he is a great guy in so many ways but he also did this. I start to feel that it is hopeless, because he makes the same mistakes over and over, and even forgets why it was bad in the first place (like when I told him several times that I don't need bashing when I ask him for comforting, amongst many other things).

And in the long run, perhaps I could forgive him but what about his friends? Am I supposed to be reminded about how he broke my heart and my trust every time they meet? Are they going to our wedding? Hell no..! Right now, even if I forgave him, I wouldn't ever want him to see them again. But that is not my choice, he has to come to that conclusion himself. Otherwise I know who he values more.

What do you guys think I should do? Give him a chance, depending on what he will do to make it up to me/make me trust him again, or just leave? I really need some other people's opinions about this...