Should I tell my fried that his girlfriend was not being abused but actually having an affair?

I have a friend (Max) who is in my major and shares a bunch of my classes and over the past year or so we have become more or less close. He recently moved in with his girlfriend (Lea) of a year and a half and since then we have gone on a few double dates with me and my partner. On one of these dates, Lea told us about a rough patch they had in their relationship and that during this time she was in a “friendship”with a girl that was essentially abusing her, emotionally and sexually. She went into quite a bit of detail and initially I obviously did not question her.

That was before I spoke to my best friend (Hanna) about this situation. Hanna and Lea were pretty close until about six months ago, when Lea cut her off pretty much out of the blue. I told Hanna about what Lea had told me because I thought it might be an explanation for why she stopped speaking to her and she was shocked. She told me that she had been a big part of this friendship group in which Lea was apparently being abused and that it was absolutely not true. She showed me countless pictures of Lea and the girl that was apparently abusing her in which they were clearly in a loving relationship (kissing, holding hands etc) and showed me messages between Hanna in Lea where Lea was saying how in love she was with this girl and that she she wanted to leave her boyfriend for her, that she introduced this girl to her mom and that her mom also wants them to be together and so much more that does not aline with any of the details Lea gave and paints a complete different picture. Apparently this girl did not want to be in a relationship right away though, which is why Lea didn’t break up with her Max. Hanna also told me about so many times when Lea had shit talked Max to her and the rest of the group, about entire nights that Lea and Hanna had spent talking about her dilemma with the two people she couldn’t choose between and so forth. At some point Hanna said if Lea wasn’t going to tell Max then she would and that’s when Lea cut her off. I now know that that was the exact time when she did come clean to Max (he had obviously noticed that something was going on), just not about the affair but about an abusive friendship that I am certain she made up. In this she has lost all of her closest friends because they all know that it was an affair and do not condone her creating this huge awful lie to hide her mistake.

I am the only person who knows Max kind of well who knows about this and every time I see him I feel awful. He has built his entire life around this girl and loves her so much. They live together, he doesn’t really have many friends outside of her because he is so focussed on their relationship and she has lost all of her friends due to this situation and her behavior. I feel awful not telling him but I also don’t know how to or if it is even the right thing to do. He probably wouldn’t believe me initially, because I am certain that Lea has created web of lies that he does not want to break through, but I feel like I at least have to try. An affair is one thing but to lie about abuse and assault to cover it up is another. And I just want to clarify that I absolutely always believe women, but nothing that Lea told me lines up with the proof that I was shown. What should I do?