Did i make the wrong decision. Can he be trusted?

I have been with my fiancé for almost 4 years, engaged for 2. A year ago I found flirty sexual messages to a woman in America ( we live in Uk) that he had sent via a PlayStation game in the discussion room. I knew he had been speaking to people in the game as he had been playing it for about 6 months, I also knew that he had been speaking to this woman. I checked all the messages that went back 6 months and he only ever spoke to her about the game nothing inappropriate and had even mentioned me in passing like, not playing tonight as I’m out with my fiancé.
Any way in July 2014 he got made redundant and we had a row that night and he said I didn’t support him,so that night he was in the discussion room talking to this girl about the game then it got sexual and there was half hour of inappropriate chat where he said if she was in Uk what would happen. I found it went mad and kicked him out, he said it was banter that got out of hand, he said there was no intent and he knew it was wrong. We split up for a month. After a month I took him back because I couldn’t physically see him cheating on me and family and friends said his personality is flirty and banter but they don’t think he would take it any further.
Till this day I still think about it and think is this cheating? Can I trust him?
All he talks about now is getting a mortgage as we renting and then having a baby, I know he is committed but does this sound like actions of a cheat, should I have forgiven?

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