How to divorce?

I've tried to divorce my husband before. But he roped me back in with lies and pretty words. He is in his 30s and all he does is smokes his legal weed and play call of duty like he's 17. We have 2 kids of our own, have his daughter full time and pregnant with our third. I'm just done. He does nothing with the kids. We don't sleep on the same bed and haven't in years. I don't feel like I'm in a marriage. More like a roommate situation. I'm 9 weeks pregnant And fed up. How do I leave for good this time? He always says he will change or go back to therapy but hasn't. I want to be done and stick with it.