My wife and I have a very difficult 15 year old son.
I guess the first thing we figured out was we needed to do the best to look after ourselves. Think of all the small things that you enjoy and do them. Start today if you can. Sometimes it is a small and simple things that help take your mind to another better place.
We actually found our son was surprised to see us going off and living our life without him impacting on us so much.
That might be a good place to start so your 18 yr old realises you can enjoy things yourself.