I feel like he’s cheating even though I know he’s not

Recently I started dating a boy who has been my best friend for the last three years, single and not dated anyone in that time and said he couldn’t find anyone better than me so why would he.

In that time though I dated someone else (neither me nor my current boyfriend knew we liked one another so we had it on the back burner) and we dated for about six months and it was an incredibly abusive, toxic relationship where he was constantly cheating.

Now I just keep getting this creeping feeling it’s happening again- but for no reason! He “gave back” a girls top and socks to me which weren’t mine and I had a bit of a go at him before he reminded me it was from boxes of clothes his parents had bought up to his (he has three sisters) and it checks out.

But now I’m typing this okay it’s irrational. I see it. He also treats me so well. I’m just scared of the same thing happening. But there’s no signs pointing to that. How do I move past the irrationality?