If there was only one piece of advice I could give, it would be to learn to pay attention to your own instinct regarding any issue and person; to do a gut check if you will, and then to trust that instinct explicitly.
If you don’t trust your own instinct, then your self-respect starts to erode, and you become prey to the influence of others.
Your gut check won’t always lead you towards making the most rational, or even polite choice. It’s not concerned with being polite. Your gut check is looking out for you, so it’s going to point you towards the best choice for your own sake, even if it seems like the most irrational choice at the time.
So trust it. Trust your gut, and start feeling what self-respect truly feels like.