Trying to understand myself as a sub better

I wanna start this by saying I am trans ftm, and have always struggled with sex/being sexual with myself and others.

I've only recently been getting into the scene. My boyfriend and I are both very kinky, and our sex life is pretty good. The sex itself is usually great, but recently, we haven't been connecting quite so well, and I'm not sure why. We had one night a couple of weeks ago where we had sex spontaneously when I was going to bed. It was easily some of the best sex we'd ever had together. I think it had a lot to do with how tired I was. Usually, I can get really in my head whenever we're intimate, and it turns me off a bit. But it was like my brain just shut off, and I was just really able to enjoy it... But since then, it's been like impossible to get into that headspace??? I don't even know how I did it before, or if it was just because of him in that moment. I don't know, but either way, I just want to know how I can get in touch with that side of myself? And I wanted to know why that feeling is so good for me? Afterwards, when we were cuddling, I found myself thinking about how good it felt to just be my partners pet in that moment, and wishing it could be like that always. I want to be a puppy, a good puppy, and I haven't gotten the chance to talk to my boyfriend about it because I'm a little afraid of how he might respond(though I don't think he would be mean.)

Any advice or even just personal connections would be appreciated. I'm just trying to understand my own thoughts because I'm very confused.