@9101transfermum so sorry. Is he depressed? Is this a change in how he functions or consistent with high school? (You mentioned that you had to help him stay motivated.) It sounds like either he does better with school, or something will indeed change and he will have to leave. I think you are absolutely right. And once over 18 you cannot force him to therapy.
If he does leave, would he most likely live with you? This will be hard if he is angry. I hope that either the college makes him leave, so he isn’t angry at you, or that he can absorb the idea that leaving is in his best interest.
A year or two of work can be motivating. And honestly something has gone awry when everyone feels they have to go to college. There are other paths but they need more support from our culture.
If your son has any talents or interests that can be pursued outside of traditional college, that would be great. College one course at a time while working is possible. But clearly he is holding onto the traditional residential model even when for whatever reason he cannot do the work.
The real question is why can’t he do the work? I don’t believe in laziness (read the Myth of Laziness). Good luck and sympathy!