Welcome to Beyond Blue and thank you for coming here and providing your post.
I guess that 4 months is quite a short period when you compare the fact that the two of you were together for 15 years. So I can understand that this split is still raw and hurtful for/to you. The missing, the aching, the memories - nothing that you don't already know and are suffering from.
May I ask what kind of help have you been receiving??
It also sounds to me that you are perhaps still in some kind of contact with the 'ex', as you say he's turned feral - and perhaps is being 'nasty' to you as well? I only guess that due to you saying that he said he'd be still friends with you, but apparently that doesn't appear to be the case.
This part if true (ie: you still being in contact with him) is going to make the whole process a whole lot slower and will perhaps only stretch out the pain and suffering that you're feeling. I've tried this myself in the past and it just hurts so much more. Trying to see the person, hoping, wishing that they'll come back around, but it only ends up in more pain - and kind of a mental torture as well. It's not until you fully make the break and decide, ok, this is it - no more contact, texting, emailing, whatever it is - it's stopping as of now. And it's something that I had to do and I told the person that I'm pulling the plug, I won't be trying anymore.
Hells bells it was super tough at the time, but it got better. It got easier - it took a while and this will take a while, but it DOES get easier. I know you probably don't think so at the moment.
But Hugbear also think of this: your 'ex' is doing drugs. I would imagine from your post that you aren't. He's the one that's abusing his body and pumping it full of awful things. You should be damn proud of yourself for not going down that path and being the better person.
Hugbear, I hope I've said something that has helped you (even a little). I really would love to hear back from you also about this.
Write here and chat away - there's wonderful caring people here.