RJ triggered even more after we had sex

So just for context, my ex was in 3 relationships before me and his last relationship was his most serious one, he loved her, was attached and wanted to marry her, and she was his first in terms of sex. They were together for a year and had a lot of memories together. He never wanted to leave her but she was toxic and eventually left him.

I, on the other hand was a virgin. My RJ keeps coming in waves. Sometimes it feels like I'm not bothered by it at all but other times, I am drowning in wild thoughts and images of his past. Recently, I spent a day at his place and we had sex for the first time (we've been together for 3 months now) and my RJ has gotten worse ever since. The way we cuddled and slept together. I can't help me imagine someone had him like this too. It's killing me.

He chooses me everyday and expresses that I am what he wants. He does everything to make me feel wanted. Says that this is the most love he has ever felt and we have so many new memories that we are making together. So many if our personal "firsts". But deep down, I'm wondering if I shouldn't have had sex. I should've thought about it a bit more. I did have this fantasy that I wanted me and my partner to be each other's first but I also didn't want to ko lose such an amazing guy to a stupid fantasy. But I'm having these thoughts that maybe I should've had my first time someone who was a virgin so I wouldn't be drowing in comparison and insecurity. Also, my RJ isn't just related to sex. I get overwhelmed over the fact that he was in love and attached to someone so deeply before me. Sex feels secondary. I also wonder if she was prettier than me. I know with time, I'll get over it for some time till it pops up again. RJ works in crazy ways.

Not sure if this will ever stop cause I can't keep living like this where I suddenly start obsessing about his past so much. But I also can't leave after getting involved this deep.