It’s happened enough times that I surprise myself by still being surprised when it happens again. I have had friends that I thought were real friends who suddenly stopped having anything to do with me when I was no longer useful to them in some way, had personal needs (and needed a friend) or said “no” to something they wanted to do that I didn’t want to do. It is a very clear indication of they type of relationship you are in when you do decide to say “no” once in a while. Either they try to talk you into it, get mad, get offended or they accept your decision with respect and grace. It’s not really a good relationship if you do not feel free to say “no”. It’s best to go ahead and get that out of the way before you get too invested in the relationship (because it really hurts to find this out after 10 years of thinking you have a friend when you really don’t).