I worry about you starting to resent your girlfriend for getting to have all the fun.
I have a suggestion that might save your relationship or might strike you as all sorts of wrong and make you hate me, but here goes: you two find a willing top, maybe somewhere in your social circle, maybe online or in a BDSM social organization, and bottom together sometimes. This kind of shared adventure can be hot, hot, hot and very bonding, sort of like getting lost in the woods together and surviving through mutual trust and inter-reliance but a lot more fun. I think if you do that sometimes, and play top sometimes, and stick with the vanilla sometimes, you'll probably be OK, provided you both take care of getting your itches scratched. Love conquers ... much.
Got a salacious subject you want Andrea to discuss? Ask her a question!
Also, Andrea is teaching! Contact her if you're interested in (sex)life after baby classes. Her new blog is at www.gogetyourjacket.com, but don't look there for the butt sex. There isn't any.