Hi OP,
I understand completely how you feel, so if you ever want to chat then just PM me, can talk about anything.
But you can't have failed your son, because he is in college and has a girlfriend, if he is staying at hers a lot it must be going well.
Your still with his dad so your still in a relationship, you say no one cares but have you tried to talk to your partner or sister at least. They probably do care.
It's so easy to tell ourselves that no one cares but how many family and friends have been on TV after someone has committed suicide and said if only they opened up to them, because they would have been there.
If your medication isn't working go back to the Drs and make a pest of yourself if you have to and get it adjusted.
Find a hobby to do in spare time, and spend half and hour each day doing some sort of self care. No excuses, doesn't have to be a lot, even just sitting reading for a little bit with some chocolate or a nice bubble bath etc.
Have you thought about maybe getting a dog? Your could go for walks, join a training/agility center, you might meet some people there.
Sending big hugs, I hope things start looking better for you soon X