How to stay fit?

So I used to be a very active person. Then as soon as I had my first kid I wasn't able to get my ass off the couch after work to go to the gym.

I get a guilty conscience leaving my wife at home with the kid all day while I'm at work that I just want to come straight home to try and release some pressure.

She's been vocal that it doesn't bother her, but for some reason I still feel guilty. I have gained roughly 50 pounds since the kid, and 30 since we got together. I just don't feel good anymore and don't recognize myself when I look in the mirror. That can't be good for my kid, and now we're expecting another. I need to desperately change and idk how.