I've been in this situation before. they're just using you and they might not think of you as a friend at all just a sidekick. i hate it when people do that. excluding others and treating them as such a doormat.
And why would you pay??? it's better to distance yourself from them. i know being alone is hard and sometimes we get used to that loneliness but it is better that having "friends" like them.
I have only one true friend. we've been friends for more than 10 years and we're so far apart but we still keep in touch.
I pray you find a friend and that your friendship lasts for a lifetime.