Is it OK to get frustrated that my boyfriend is so Beta?

One of the things that made me fall for my partner was the fact that he is so sweet and sensitive.
I quite like/d being the more dominant ( that's not the word I want to use but I can't think of another one) protective one.
I like feeling like the Alpha female. I don't know much of that I am in general, but my relationship kind of puts me there.

He and I have a three year old and I'm 18 weeks pregnant. My daughter isn't his biologically, but she may as well be, and I am hugely protective of my family. There isn't a length I wouldn't go to... but sometimes I feel I'm on my own with that. Physically, my boyfriend is bigger and stronger than I am, but he doesn't make me feel safe, and sometimes I do need to feel that.
I feel like if someone ever broke into our home, I'd be on my own with that. I'd go for it, anyone would, but it's not a nice thought.
We rarely solve anything when we argue. He ends up walking away, and I back down because I feel too guilty. It's like kicking a puppy.
I don't feel like this all he time, but occasionally I get frustrated. Sometimes I just want/need some assertion from him, but it's just never there.
Is it OK to get frustrated that my boyfriend is so Beta?
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