...I would say that if in this case, you feel down or worse when talking to them, then it's a toxic friendship. When they make you feel like less or like you don't matter, you need new friends. A way to end that friendship, depending on who you are as a person, is to distance yourself from them until you can slip out of the friend group(not recommended) or just tell them that you don't feel comfortable being their friends, and leave that way.
You may easily find answers online. Many people have written articles surrounding the problem of toxic relationships. To try to simplify, what makes a relationship toxic, by definition, is in which one person gets all the joy and the other person is harmed by the relationship. Articles will give signs of a being in a toxic relationship as "losing energy", feeling judged, and lacking trust. Personally, I'd say any relationship, toxic or not, that involves one or both people lacking trust or feeling like they're losing something in himself/herself is a relationship that needs to be changed.
If you ask me, you shouldn't go straight to ending a relationship only because you think it's toxic. I think one should first try making it not toxic before they make it not a relationship. I say this because usually the person causing the relationship to be toxic doesn't even know they're doing it! If you feel you're in a toxic relationship, at least give the other person a chance to change for the better. A lot of people are new at making friends or being in love. If convincing them to not be toxic isn't enough to fix a toxic relationship, then don't waste your time and find a polite way to separate.
That's just my advice. You're free to disagree. PM if you want me to go further or read the other people's comments. Best of luck to ya!