I'm sure that has a lot to do with it. They may also feels sorry for their dad and think he's lonely and needs company.
FWIW, my older son once commented to me that he respected the fact that I said "no" to some things his dad allowed. His dad is a good guy, but he has a harder time saying no to things.
I know it's hard not to feel hurt by it, but kids are very selfish beings, by and large. If you keep doing the next right thing they will eventually come around, I'm betting. Boys mature later, and it sometimes takes a while.