I'm so sorry you received such an ignorant response, it seems that some less mature men can't discuss lesbian relationships without feeling the urge to sexualise it. Such infantile behaviour genuinely doesn't represent the majority of us here.
I agree with the advice given above, this has evidently become a toxic relationship which only one party, you, are willing to repair. Walking away from somebody you love will be one of the hardest decisions you'll have to make, setting aside the guilt and resisting the urge to answer those late-night calls begging for reconciliation, it's emotional hell - but eventually, it's empowering.
Walking away from my toxic, cheating, manipulative, abusive ex-partner was one of the best decisions that I ever made. It took me months before I was able to look back on her behaviour and see it for what it was; even longer before I started to feel strong again. I had decided that I was worth more than her behaviour, I felt empowered with self-respect, I felt confident to set boundaries in future relationships, I knew that I deserved better and I was no longer afraid to walk away from a bad relationship, it was a valuable life lesson.
I know that there are obstacles in your way right now that prevent you from simply upping and leaving, but if you're ready to walk away then now is a good time to start setting some personal boundaries. Try to spend more time with the people who care about you and are emotionally supportive, you mentioned your sister in particular. Create your own personal sanctuary and visit it every day, I know that sounds a little ethereal but it can be as simple as taking fifteen minutes or half an hour to yourself each evening and practising a simple mindfulness meditation, or spending that time doing a hobby or even on doing your hair or makeup; it's time dedicated entirely to yourself, I found it life-saving in the run-up to my breakup.
Regardless, it sounds like an awful situation and I'm so sorry that somebody you love dearly is hurting you like this, it's a long and difficult journey, but as you begin to traverse it, you are ultimately going to find strength that you never imagined you could muster.
Hugs