This applies to all types of relationships: from friends to significant others.
When people are unhappy with themselves, they tend to hold a certain amount of animosity towards those who are happy with themselves. They almost instinctively try to dull their shine. Are you a shiner, or a shine-stealer?
I share this from personal experience. I allowed someone to dull my shine and I had no one to be mad at, but myself. I was happy, headed in the right direction, and excited about life until I began questioning myself. I let someone question me and who I was for far too long. If you hang around negative energy, it eventually latches on to you, too.
It’s not that they are bad people, they just haven’t found their way yet. Give them a fair chance before you just cut all ties. Sometimes people go through hardships and they take it out on all the wrong people.
My best advice is this: once it starts to affect your mental health and/or happiness, it is time to let go. Be honest, tell them the deal. Be selfish and put yourself first. That’s loving yourself.