Why do people feel like they should backstab?

People backstab because they are scared human beings. You might think they know about life therefore you are not expecting them to stick a knife in your back. But the truth is we are all messed up humans in the head and all we care about is ourselves. So you can't to go through your whole life expecting none of your friends to stab you in the back every now and then.

However, you should learn to forgive. Because resentment of these backstabers can ultimately lead to your death. For resentment and unforgiveness against people brings nothing but horrifying results to your life. Just let it go, Don't talk to them anymore if you have to. But dont hold it against them. But if you can then forgive them.