I too was surprised and very hurt when some close friends provided little support and amazed at the kindness of others when I had not expected it. I cherish those kind people. As you say, while the truth hurts a great deal, ultimately it is worth knowing. Several years down the track I have forgiven them somewhat, realizing they had their own problems, have limitations as people like we all do, and also didn’t care as much for me as I thought they did. Turns out many people are so fascinated with their own lives they don’t pay much attention to anyone else’s. They can also be pretty demanding about wanting you to focus on their lives. Those that do care about others are rarer and wonderful. There are other people out there who can become your new friends.
It’s worth saying to others who want you to do lots for them and you don’t want to, I am sorry I would love to help but since my cancer treatment I am just not up to it, I get so tired some days. There is no answer to that.