I 20 Trans F am worried about my 20 Cis Male boyfriend who erp's too much?

I have never posted on Reddit before, nor am I a big Reddit user, but I need help this is a tricky one. I 20 TF am dating a 20 Cis M. He's the quiet type, very nerdy with games, and I love it. I recently discovered he has a pretty big history with Erotic role-playing fictional characters. I've asked him once about it, and he denies it. It never bothers me that he ERPs because it's all fictional, and im more the romantic type, but when I was at his house we were watching YouTube videos on his phone, and he swiped up, and I saw one of his role plays. I didn't say anything at the time, but brought it up later, and he explained that it was a bot someone else was using in a Discord server. I have used Discord for multiple years and know what direct messaging looks like. I brushed it off and proceeded with life, but a few weeks later, I saw the same type of messages with a different other user. I asked him about it again and he denied. Noww the problem isn't that he is erping, now with him I, it's that he's actively denying it while doing it in my face, I want to find a way to tell him I know and i am hurt that he doesnt feel he can talk to me about it, but in a nice calm way that doesn't embarrass him in any way or scare him. Got any tips?
p.s sorry if my writing is bad again im not a writer in any way just looking for advice. other than that hes the perfect man for me and treats me so amazingly i just want to find a way to communicate on this