I will try to be brief. I've been in a relationship with my partner for 4 years, seeing him casually for more than a year before that. We have been living together for a year, prior to that we spent around 3 nights together and 4 nights apart every week. The relationship has progressed slowly, something we both wanted.
A couple of weeks ago he left his Facebook account logged in on the laptop I use for work. My curiosity got the better of me and I had a quick look at his messages. I know that is bad form and I shouldn't have done it.
Messages from a couple of months ago from an old FWB of his caught my eye and I read the thread. He hadn't replied at all for the past year and the year before that he had only replied to general messages and stuff about his music but had ignored anything suggestive. She seems to message him a couple of times a year.
They have known each other for years and grew up together, their families know each other. She is his age, I am younger. I have met her a few times, we have a couple of mutual friends.
In mid 2018 there was a few messages exchanged where she sent him a picture of her in her underwear and a bit of sexual chat, from both him and her. Initiated by her. There were a few messages a couple of months before that where she was reminiscing about when they used to sleep together but he didn't really engage with the topic.
I was furious, called him out on it and told him that I read the messages. He apologized, said that he knows he shouldn't have done it and he had stopped replying to her years ago. He said that it was just the messages I saw, there was nothing more than that. He said that he had stopped sleeping with her before even the casual thing with us. I believe him, and he does seem to regret it, but I'm pissed off that he even engaged with it as much as he did during our relationship.
As annoyed as I am about it I still love him. I have accepted his apology, and agreed to let it go and move on. I haven't quite moved past it in my head yet though, and I can't decide if I am being ridiculous for wanting to overlook it.
Would you forgive and move on or bail on the relationship?