I think my boyfriend is a sissy. Would love some advice

Hey guys, I’d like some advice. My boyfriend and I have been dating for a while and I’m trying to get him into some kinks because we’re kinda vanilla. The other I found some pictures on his phone on total accident of him dressing up as a girl and a bunch more with crazier things. Like obviously it doesn’t bother me, I’m bi myself. But I didn’t know he had this secret side of him, he’s never told me about it. I don’t exactly know what to do. I’ve known he’s pretty submissive sexually which I actually really like but I didn’t know anything of this. I’m still learning about what a sissy is but I’d love some more advice going forward