I've never had somebody offer to be there for me, then disappear for a few months. Maybe the people you were hoping to rely on found themselves in need in a way that prevented them from being there for you.
Sorry you are surrounded by unsupportive people. Make a better support network for yourself, including a therapist who is trained to help you.
Don't expect casual friendships to bear the burdens of your mental health. It's your responsibility to take care of yourself, nobody else's. Any help offered is more than is required by others.
In any case, the situation you are describing does not apply to what I said. I was talking about honest offers from people to help and how being endlessly in need will eventually use up the goodwill offered.