My fiancé (21M) and I (20F) have been together for 2 years now and everything has been great up until this last weekend. We were talking about a threesome and both agreed for him to find someone on here. We had found someone and were talking back and forth for a day or two when I wanted to see what they were talking about. On Saturday morning while he was still sleeping I took his phone to go look through those specific messages and that’s when I found these messages to some other women. I won’t say specifically what was said but they were pretty explicit and he had sent some photos to one girl. He had messaged the first girl around 3 am while I was in our room asleep and then came into the room to cuddle and go to sleep after he was done with her. The other messages I found were worse imo and had been going on for days, at least that’s what I thought at that time. When I woke him up to talk he said that it was just porn to him, didn’t mean anything and that he didn’t want to wake me up for anything since he felt bad for waking me up. When asked if there was anyone else he was messaging he said no. I believed him and we talked for a while after that and I thought we were good. The next day we went to a friend’s place to hang out for a bit and then we went home and he took a nap. My anxiety and paranoia over this whole thing took over so I got his phone and went through everything and found even more things than I thought. He had all these pictures of other women and was even asking for pictures and videos from an old friend of his that was selling them. I went through those messages and realized it was the same girl he went to help out and give money to because of a situation she had a couple months ago. I then went to see what apps he had and realized he was paying for a subscription for a toy we have that lets you connect to it and control it with your phone. I just recently found that toy since it was hidden on the top shelf in the bathroom since we moved into our house a couple months ago. I logged into his account and found all these women he talked to and saw that the one he had been messaging for days was from there and it had been going on for months. When I had originally asked him where he had met this girl he said he couldn’t remember. They would only talk in the early morning and it was all very sexual. They talked about all these toys that she’d love and how he would do her all while I was either in our room next to him in bed or while he was in the living room. I was heart broken thinking about all these things and he insisted that this didn’t mean anything to him and didn’t realize that this was a boundary I had. I’ve told him that he has to prove to me that he wants to stay in this relationship and not just because I want him to. He’s told me countless times since then that he wants to stay with me but if I didn’t want to he understands why. I don’t want to leave him, I’ve never even thought of leaving him. I just want to know how do we go past this? What should we do to work this out so it doesn’t come up again?

TL;DR I caught my fiancé of 2 years messaging other woman and buying pics/vids from an old friend that owes him money. When confronted told that none of it mattered to him and was just porn to him. He wants to work this out and I do too but how to we get past this?