Welcome to almost every married man w/ children's life. Stay with her, cheat or leave. There are only those three roads. She's never going to change. Your dick is designed for shooting sperm. Once it has blown it's load, the last thing it feels like doing is having sex again. Once the vagina has popped out a baby, her body has now blown it's load in a way and her attitude towards her own vagina changes. She is done using it as a sperm-bait.

The baby changes them, man. It's difficult. We all deal with it. That's why a lot of dudes out there are on their second marriages. Had kids with one, entered dead bedroom, revolted and found someone to have good times with.

Like Metallica once sang, "Sad but Truuuueeeeeewwwww"