First, I am of the opinion that his weight could be a part of it. If he's very overweight, sex may be physically very straining for him. If he's even only slightly overweight, he might have body image problems that could cause a lot of problems for him mentally and, through them, sexually.

Second, he wasn't as sexual as you to begin with and he expressed his strong desire to be a father. Now he's not being very sexual and he's being a very fatherly figure to your daughter. It seems like he's being very much like what you expected he'd be like.

As for improving your sex life, there's a lot of great advice. Definitely tell him you need to have more sex, and that you want it to be with him. Express to him how important it is to you.