Your feelings are human and understandable.
Remember, if your DH still has his drink, drugs and women habit he will be burning through that inheritance money at a fast rate. Easy come, easy go as the saying goes! So there's that to think about.
I have a really good relationship with the DCs and plenty of friends
Something that your ex probably doesn't have? Alcoholics/drug users rarely have true friends - just people who share their bad habits and addicitons.
I bet it only appears on the surface he is having a good time, while you are building something real and sustaining in your relationships.
See your doctor about getting back on track. Perhaps some counselling and/or anti-depressants are needed? Use your sick leave to search for another job - getting the right job can work wonders and staying in a miserable job really takes its toll.
When you feel a bit stronger, see if there is anything you have always wanted to do that would be possible to start now? A degree? Could you get a student loan and be a full or part-time student? I don't know your financial circs, but take the time to explore ALL options however "out there" they may seem at first. You may be surprised.
When you have the most fulfilling life you can, you will stop thinking about your horrible ex. The next you hear of him will probably be when it all comes crashing down for him (i.e. money spent, addiction tightening its grip) and you will probably feel more pity than anger for him.
Take care, OP. I know this can be hard. 