I (33M) found out my partner (30F) Cheated on me 4 months into our 5 year relationship, need advice and thoughts on the situation.

My partner and i have been in a serious relationship for the last 5 years. We own a house together and have plans to be married and have kids together (and a dog).

We go on each others phones occasionally sometimes playing each others apps or look something up quickly or lending it if one of us is out of charge. Very normal for us to be on each others phones and would not question each other if they were

When we met she was in her “slut phase” (her words not mine). We talk and laugh about the the people she was talking to at this time as she had some funny experiences and stories from back then. One night i was curious as to the kind of conversation she had with those kind of people so i looked through her messages from back then. ( I am aware that this is a massive breach of privacy but at the time i could not help my curiosity). I found some saucy chats she had been having with a couple of guys and thought nothing of it until i looked at the dates and thought they were close to when we started dating. I checked on my whatsapp and it indeed was months into us dating (4 months give or take). One chat was after i had left hers that very day while we were living away from each other (1.5 hours travel) and that evening she had been talking to the guy after i left and arranged to go round to his late at that night last minute, the language was far more in depth than that but i dont want to type it out, you can all imagine what they were saying to each other (sexual and suggestive). The text the next day from him was “sorry i fell asleep so quickly”. All of these happened after we were very official and even gone on romantic holiday away.

I sat her down and said i had messed up and looked through her messages and found some things i thought we should talk about. I explained what i had found and how it had happened into our relationship. My partner has issues with ADHD and said she could honestly not remember any of this. She broke down and said she can remember it at all, i told her the dates and even meeting with a guy after i had left her that day etc. She said she may have been talking but never in a millions years did she sleep with them as she would have remembered. She said she was a completely different person back then and after a small hiccup 6 months (long distance was hard at the time, then we moved) into our relationship she had been totally committed to us. I comforted her and said i forgive her but cant get it out of my head.

For as long as i have been with her we have both said we were 100 percent anti cheating and if it happened that would be an immediate end to the relationship. From my stand point she 100 percent cheated on me at the start of our relationship but i have been with her and wanted to spend the rest of my life with her.

Things have gone back to normal in the relationship since that and it feels like we never even had the conversation. I keep thinking back to it and I’m finding it hard to trust a woman that i have trusted unconditionally for as long as i have known her. I also think of the holiday we shared together which was one of the fondest memories of my life up to this point (as mentioned before we went before she cheated, when i met her i had just not long gotten my life together after heavy mental health issues).

Sorry for the long post but i needed it off my chest and to ask what other people thought. Can people change, does 4 months outweigh 4.5 years?

I am wanting to start therapy so i can talk it through with a professional but thought why not ask others while i wait.

Thank you for reading

p.s I am aware that i am also at fault for looking at the messages