I've been betrayed by several Christians who I had thought were friends. Our pastor completely stopped talking to me because we had to stop attending church due to severe injuries I sustained. It made me really see what is what. Then another Christian did something truly devilish. Then a Christian I had been friends with for years showed me that her friendship was shallow. When I was injured she never visited and I saw that she treated her church friends well but looked upon me as "if I get the time I'll answer" - she actually said that. So I stopped contacting her and she kept emailing me so I did to her what she did to me and she didn't like it and completely cut me off. It showed what she truly is
David in the bible talked about "mine own familiar friend" - and I wondered how many other believers experienced betrayal from other Christians? I think that somehow I missed the boat in finding friends who wouldn't backstab but I listened to one of Charles Stanley's sermons and he said that most people don't have a lot of friends. I guess he's in the position to see things in an entire congregation. I heard another pastor who said "some Christians you can't turn your back on" and that has been my experience. When things are going good people want to be around but when you fall is when you see what people really have in them. Have others experienced this?
The people you speak of are not true Christians since true Christians never do such things. If they did, they automatically cease to be Christians until repentance. Some people who claim to be Christians are actually reprobates who live their lives outside the Bible and the word of God (even if they verbally repeat words from the Bible without backing with actions), following godless ways of thinking and living like tribalism, paganism, or worldly-desire-chasing to name a few.
The key difference between a Christian and a non-Christian is whether someone has the heart to rebuke their brother when they sin or not.
If they do, it means they are not attached to this world and care more about their brother going to Heaven and avoiding Hell, thus putting God's obedience above worldly matters and feelings, and following Jesus Christ's command to rebuke their brother when he sins.
If they don't, it means they are actually attached to this world, not the Kingdom of God, and thus put their "feelings" above serving God, and don't truly believe in Heaven or Hell since they allow their brother to perish in the after-life as a result of not rebuking, and don't love or fully accept Jesus Christ for not listening to him.
Godspeed.