@newlife123: Thank you for the constant replies. This is my first ever post and you guys have been ridiculously helpful! 🙂

That’s true – the truth is the ex who cheated on me didn’t mean half as much as this girl and that’s why I guess it was easier to get over. I’d be lying if I said it didn’t hurt me but it was much easier to leave the relationship.
I can handle arguments in my relationship but trust is something I value the most in a relationship. I’ve always stood by the idea that if the girl I’m with hurts/shows me she doesn’t want me in any sort of way then I’m done. But I almost feel tied to this girl, I’ve invested a lot of time and effort.
What you and him said is very true; the hurt was unreal and very painful to be honest.
The first guy: thinking I wasn’t good enough or that I was second choice. And this guy at work: thinking I was being replaced and she enjoyed the company of another man.
The pain is real and that’s why I find it hard to get over especially that it’s the second time it’s happened. My question is how do I let go and move on in this relationship without minimising the pain? And surely my overthinking has played a part in it? But I’ve told her I didn’t make up the scenarios all by myself.

Thanks Adam