I'm sorry you find yourself in this tricky situation. Amazing what we can do when constantly drunk. Then throw in heart break and rebound. Ugh.
So you've only known him 18 months so ya haven't been together too long. Do you own things jointly? Did you have a child? I'm not an attorney (you really need to consult one) but I think you just file and take it from there. I know being on good terms is what is easiest but that may not be possible based on what you've written. Is the place you are in yours?
Well, best of luck. Spend a couple hundred on a consultation. Some attorneys may do the first apt free as well.