It changed me definitely. I found out about a two year affair with my then DP just after we bought our first house together. There had been many instances of my gut instinct telling me something wasn't right but I didn't ever have the confidence to confront it, didn't want to face it I guess. Whenever I did confront smaller things he managed to make me feel like it was all in my head.
I found out, I hated him and I moved out but still did stupid stuff like agreed not to tell his family the reason reason for our split as he didn't want them to view him differently (WTF). I even tried being friends with him until I found uut there months later that she was pregnant (he said they had split too).
It made me stronger funnily enough. I absolutely trust my gut now and am not afraid to question things that feel dodgy (not that I have had many occasions I've had to do that). It made me look for an entirely different type of man. I'm hindsight he was so weak willed and attention seeking that he was a sure thing to have an affair. My DH now is the total opposite, we share similar views on fidelity and divorce etc know that an affair of any type would be an immediate deal breaker for either of us, even though we have two children. I can honestly say that I do trust him completely despite my previous experiences. I also met him in an entirely different environment where we both volunteered for an amazing charity showing me how selfless he is. To this day he is ALL about me and our boys and does anything for us.
I have to say though because of all of that if my DH ever cheated I would be absolutely blindsided. Totally floored by it. I think that would absolutely change me irreversibly and I would never trust again, especially as I could never understand how someone could do that to their children too.
I was very open with my DH about my past experiences and how it may lead to me being insecure at times, especially as he had many many females friends when we met, who he saw for dinner etc regularly. I found that a bit strange at first but naturally as our relationship developed the regular meetings reduced as he was out on dates with me. Those friends and their now husbands are now also my friends.
Our experiences can help but shape the people we are.
They have also led me to totally cutting off my sister in law after she cheated on my brother. I have no time for cheaters!