Your suspicions are perfectly valid, I promise. Here's how to tell if there are serious problems in your friendship.
1. They never make the effort to see you
Friendship is a two way street, and you should not be feeling like you're doing all the work.
2. They never adjust their behavior even when you told them multiple times how much it bothered you
If they won't even take your feelings seriously, are they even a good friend?
3. They're not happy for you when something good happens to you
A real friend would celebrate your successes with you.
4. They are low-key threatened by you
This isn't good. You should be able to see each other as teammates and not competition.
5. They make you feel crazy for demanding basic respect
The worst is when you lower your standards so low that even basic human rights feel like a luxury to you.
6. When they have a problem with you but don't talk to you about it directly
This is so passive aggressive and not needed.
7. They don't care that they're causing you pain
In fact, you suspect that they might actually enjoy how hurt you are and take pride that they were the one who did that to you.
8. You feel like they don't care about you as much as they used to
Sometimes your instincts might actually be correct.