Not sure how to feel

So I recently found out through a coworker that the guy I’ve been dating for about 2 months now (we’ve been seeing eachother about 4 months now) was talking to another co worker of ours previous to me and him. Here’s a little back story. They have quite a few mutual friends, and she had a boyfriend the whole time, however apparently the boyfriend is constantly cheating on her so she would always go to my guy when shit was rocky and he really liked her a lot but she broke his heart by always going back to her man. Im aware there’s always gonna be someone before you, and in some cases there’s gonna be someone after you. But here’s the part that gets me. He never told me about it, when we first started talking he told me he had recently just got out of something but the girl broke his heart, she really hurt him. And when I asked who he said “oh just some girl I went to school with.” Also on a couple of occasions (prior to us becoming a couple) he would talk about her casually like “ oh yeah well she’s not very loyal she messes around with guys too but I heard that from a friend” or there was another time he mentioned that he was upset with her because she had taken her boyfriend back…

When I found out I definitely confronted him but i did in a terrible way. We were both at work and I brought it up and his face looked as if he seen a ghost, but he admitted it. I was pretty upset and I told him he definitely should have told me. I even went as far as almost breaking up with him. His reasoning was he didn’t want me to think anything, and it wasn’t important. He said after he met me shit changed i motivated him to do better this and that everyone notices how happy he is ( and I do believe him because prior to me he would always drink and smoke, he was a sad boy) he seems like fairly loyal guy especially to the people he cares about. And he’s a sweetheart to the maximum.

However I still can’t get the thought of maybe he didn’t tell me because there was still something going on, there’s a couple times that I can think of where I walked in the break room and they were both in there not even at the same table or anything but still in there together. And sometimes he’ll text me to take my break with him. So I guess I’m just a lil paranoid that they are sneaking around. I have no reason at all to think that. As in he’s never given me a reason to think he’s cheating or talking to other girls

I do however feel like that triggered me because my ex would always be messing around with tons of girls behind my back and when I’d confront him he would deny and deny. My new guy is nothing at all like my old guy. He treats me well he’s always checkin in on me to make sure I’m okay. He really seems like a good guy. I just can’t seem to move on from this and I’ve talked to him on multiple occasions about it and he tells me there’s nothing going on he would never ever do that he would never do anything to hurt me, whenever I need just tell him how I’m feeling and he will do everything to reassure me that I’m all he wants. And we talk about our future quite a bit like becoming successful and growing with eachother. Like I said I’m just having a hard time moving on. I’ve been getting terrible anxiety at the thought of them working together. Or even when I’m not hanging out with him I get scared that he’s out with another girl. And like I’ve said he’s never given me a reason to think that. Prior to me finding out i never would have felt any type of way.

Does anyone have advice to maybe help get over this insecurity, am I worried for no reason ? Should I be worried??