I want to leave, but my conscience bothers me

I've been with my wife for almost 20 years, married for 10. Everything was fine for the first few years, but for the last five, we've slept together literally three or four times a year. And in the last year, not even once.

She's a good person, but she's let herself go lately. She's gained weight, eats a lot, and drinks alcohol. I've started working out and losing weight, and I've suggested she do the same, but she refuses. I've tried to have sex with her a couple of times, but she's rudely pushed me away.

We basically live like roommates - sharing chores, worries, and all that. No romance, shared interests, or anything romantic.

I'm really ready to leave. Especially since this year I started a close relationship with a coworker. We joke around, get to know each other, and she's showing interest in me - more than my wife. There's no romance or cheating between us. But I'm definitely attracted to her. But I'm not sure it'll work out, especially since she seems to be seeing someone else. The very fact of this interaction with a colleague seemed to awaken me. It turned out that I could be interesting to someone, evoke emotions, positivity. And I began to wonder, what if my life hadn't ended there? What if there was still a chance to find something new in it?

Unfortunately, my conscience bothers me. We don't have children of our own, but we do have a stepdaughter. We have a good relationship, but there have been conflicts and arguments. She's quite a selfish person and does what she wants. And this year, she decided to have a child without being married. She broke up with the baby's father, and now she and the child live with us.

I'm not against having a child; I love children. But I feel like I've been presented with a fait accompli. As if no one asked my opinion at all. As if I'm a nobody.

I'm confused and don't know what to do. I want to move out, live alone, and figure myself out. But at the same time, leaving my family, leaving my wife and stepdaughter alone, seems wrong, rude, and bad. I need some advice