I'm really sorry you're going through this. We all change after having children -- don't feel bad about that. IMO my responsibility to them far outweighs my wants, and this has necessarily made me a more serious person. I expect my dh sometimes wishes I would "lighten up," too, but I think he overall is glad that I serve as the grounding force. I think this is a maturity issue to a large extent and that, perhaps, you have matured more than your dh. I also think it's really hard for a couple to stay at the same space mentally/spiritually b/c we all change as we're going through life phases -- I can only assume this would be even more of a challenge b/c your relationship began when you were so young.