A little embarassed to admit this.

My boyfriend and I were watching a japanese movie a while back that we'd never heard of, and at one point, the main girl's evil boyfriend had tied her hands with his belt and gagged her while he had her. I was busy thinking, "I didn't know this movie was going to be so graphic," when all of a sudden, my boyfriend slams me onto the floor, rips of my pants, and clamps his hand on my mouth. i was so surprised at how FAST it had happened, but at the same time, I wasn't scared. My boyfriend takes good care of me and our son, so I knew he wasn't actually going to hurt me. However, this was extremely out of ordinary for him, and before I knew it, he was all over me.
Some things to note: he claims he's never watched porn because all he can think of are how dirty the girls look, and how fake everything is. He's usually the one who takes the longest to finish. And he's the least creative lovemaker, but I have noticed he gets more excited whenever he's the one in control.
About a week later, without any real reason, he pinned me against the wall and proceeded to cover my mouth and blah blah blah. What's a little bit embarrassing was how much I liked it.
Should I be worried if I let this become routine? Is he going to turn into some kind of psycho rapist or is this just him finally finding his sexual niche?

He gets excited about being in control, being dominant. He's probably a bit into bondage so it's something worth looking into if it works for both of you - if it spices up your sex life why the hell not?

I'd be a bit worried since all this happens all of the sudden, without any warning or previous discussion...I don't like 'out of character' actions...

Since you liked it (and there's nothing to be ashamed of there) I'd say go with it - but you SHOULD discuss it at some point. You need a safe word. You need boundaries. You need rules.

Stay safe, have fun.

Adding spice to your sex life

Nothing wrong at all. Sounds fun. I would talk to him about it and have a safety word...especially if things develop as they seem they might.

Make sure that communication happens, and that it happens BEFORE you get into the scene. Also make sure you explore your feelings on this new form of play, and don't ignore them. If you like it, great; if not, that's okay too.

Just as well you have no problems breathing through your nose.

I would be very careful. Things like this can get dangerous.