Hi, OP -
I am so sorry to hear this. I am glad your DS is home now. Recovery needs to be his top priority, and salvaging what you can financially of this year can be yours. @AelinAG knows what she is talking about.
Your DS is lucky to have you.
You say the lack of friends was an issue and that is certainly understandable, especially for a sensitive soul. However, FWIW, four weeks is no time at all, particularly if DS was, like most, somewhat scattershot in his approach to friendships.
The question of whether to return to Durham is tricky, assuming he has the option - and of course the choice must ultimately be his. Both @Seagulldancing and @MargaretThursday make excellent points of different kinds.
I wonder whether having had a taste of Durham would enable DS to plan a more predictable and hopefully reassuring return? For example, he could plan some clubs and societies to check out. He may now have a sense of how things work at Durham, which can feel reassuring. Etc. All of this matters.
Is DS able to access medical/psychological help over the coming year? A professional may be able to help him figure out the best way forward. None of us can know whether he can thrive at Durham and I agree it could go either way. He only belongs there (for his own sake) if he can.
I am sorry to say my understanding is also that this is the use of the standard gift year. However by going through the GP and his Vice Principal DS is optimising his chances for a successful mitigating circumstances petition later if necessary. Still difficult, though.
In brief, at least he has begun by doing this right. I very much hope he can get the help he needs for a good recovery and good decision making. Very best wishes to him.