Your son has to realise that his BF had other sensible choices.
BF had his own parents to turn to for care, nursing, any extra funds he needed, transport, and good sleep….a space to recover.
He also had the benefit of a second study bedroom in his Uni halls of residence with his BF staying with him to care for him and nurse him….a space to recover and study.
He rejected both of those choices in preference for a bed at your house with you nursing him, feeding him, ensuring a quiet space and your son fussing over him and ready to meet his every demand.
As it turns out, BF didn’t need assistance in his recovery at all because with the removal of what you could provide OP, he rejected help from your son.
At nearly 19, BF has to decide exactly what it is that he does want given what is available to him, whether that means finding a bit of humility to make up with his parents (no doubt the hand that feeds him as a student), settling down to concentrate on his studies, finding a job to support himself, or to continue to try to manipulate your son into providing more comfortable, fully paid home comforts, transport, and no doubt money for his extra weed needs.
He has rejected your son now that you have cut off the comfortable home comforts.
Now it’s up to your son whether or not, given that rejection, he continues to offer himself as available to be at BF’s beck and call.
You have done well to illustrate so clearly to them both, the bare bones of their relationship. A lesson they both needed so that they can now decide how to move forward …together or not.
I’m sure you are hoping they both think hard and make wise decisions and start to value themselves and their own families a bit more.