Some people are not equipped to deal with someone who is having a nervous breakdown.
Some people, as @Coloma pointed out, get wiped out emotionally, themselves, after listening to years and years and years of negativity and giving endless advice and support, when the other person doesn’t do anything to help herself and goes round and round and round in circles coming up with reasons for why the advice is not useful, and constantly mis-understanding what the advice giver is saying.
Most people are neither doctors, nor therapists. It’s not wise to assume that any of your friends, no matter how close you once were, should step into that role.
If this person, to whom you are referring, is someone with whom you are/were falling in love with, and he didn’t share your feelings, then he would have been the worst person for you to confide in with your feelings of anxiety.
It doesn’t matter how close you are to someone in the good times, some people, simply cannot help you in bad times. Hopefully those people can attempt to steer you towards people who can help you, but they may not even know where to steer you and they can’t help you either.