I'm sorry you're having a bad day. The lows are really tough. And I understand what you're saying. My wife and I have had this conversation. I'm not going out on purpose, but if I have a tumor, don't you dare keep me alive one more day than I have to be. Is that sick or what? But it's the truth. And thankfully, she feels the same way.
It does get better. Don't give up on therapy. Maybe a different therapist, but therapy is the only way I know to get out the other side of this big, black thing we're in. For me, it's letting go and feeling the pain, not being the tough guy--that's what helps me feel better. The pressure builds and builds until it comes out anyway in a lousy day full of conversations like you had with your wife.
I know you won't fall apart completely. It is possible to do this work and feel better. And I don't think it's "weak" to feel hurt about the mess some jerk chose to make of our lives. It's mourning the loss of the decades of our lives. I lost the thought of having any family at all, the hope of having my mom say that I'm OK. I've lost a lot, but look what we've gained. People who we can be close to. They know our pain, and they still like us. Those are the real friends.
Hang in there. And I think the fact that you care what kind of father you'll be shows that you'll be a good father.
"This search for the truth--it's not for the faint of heart."--Goren on 'Law & Order: CI'
"The former things will not be called to mind, nor will they come up into the heart."--Isaiah 65:17