I've been reading this from the beginning and I'm going to go against the grain here a little bit. OP-why are you letting your child dictate to you in this way?
I completely understand doing so at first because of the situation but it seems to me that you all tied yourselves up in knots trying to rescue him and have made it abundantly clear to him how much you care and that you want him back and he is using your emotions against you.
I am sorry if this is controversial but I wouldn't buy into his victim narrative-and I would say exactly the same if this was your daughter instead of your son. His GF basically threatened to kill you and he is still choosing to be with her and you are facilitating this with your behaviour.
In your shoes I would let him know that you love him and he always has a home with you (as you keep doing, which is great), but I absolutely would not be driving him around anywhere and letting him call the shots like this. I would let him know that I will be happy to keep driving him to and from his activities, but only from and to his HOME-i.e., he needs to make his way to your house and he will be dropped back to your house. You are not a taxi. I would not send him any additional money to support him living away from home, and I would carry on with life as normal.
You have another children don't you? Don't let this impact your entire family like this. Have your days out, holidays, celebrations etc. as normal. Always invite him but don't let him dictate the narrative or affect things on the day.
If you are not careful, this will drive a wedge between the other members of the family too-why should the rest of you live in a horrible, stressful atmosphere whilst he gets exactly what he wants?