because you like seeing her excited...that would be my guess
Simple answer; you are a cuckold.
Careful. You do not know what your watching. Look at "Toppy".
listen to benferrell man, be more assertive. start talking about types of women that turn you on, see how she likes it
We like a hard man in more ways than one. Eg; The Rock.
I'm clueless, if you ever figure it out then send me a note.