Gently, I think the relationship is already damaged because you have repeatedly told this person your situation and they have repeatedly ignored you. Your attempt to self-help was thwarted when the group kicked that person out. They all know you are drowning because they’ve told you that you were disrespectful in asking for help or to hand things off. These people are not your friends, these people are disrespectful, they are dishonoring you, and they are not valuing you whatsoever.
At this point, there is nothing to salvage here and you need to simply send an email of resignation, effective immediately. If you have access to the email account, set up forwarding to someone else. If they have your phone number, set your voicemail to say that, if someone is calling for x, the person to call is now y with y’s number.
Gently but firmly, enough is enough. They are vampires and are sucking the life out of your time, your thoughts, and your paid job. They aren’t clueless, you’ve been vocal and clear (yay for you!!), you have to stop this and the only way is to cut it off. Your mentor may need time to process before coming back ground or you may find out that your mentor isn’t as invested in your success as they once were or as you thought they were.
I’m sorry you’re going through this and I am preemptively proud of you for loving yourself enough to prioritize your health, your wellbeing, and your career ahead of those who mistreat you <3