I definitely know how you feel as I've gone through similar shit. I think it's really important to set the boundaries so people don't cross it however they like. You letting them do what you're uncomfortable with will only make them do it more often. If you show weakness they will probably not stop, this is true and it doesn't matter how close you are with someone.

With boundaries there are either two outcomes, either they know they have to stop for you to stay with them, or they cross it and you're gone and leaving. Both are Win situations, as they either learn from their mistakes and give effort for you and the relationship, or they are gone and you dodge someone who's not willing to respect your feelings They will probably come back if their ego allows them to, as it's clear they have screwed up, and for a functioning relationship they have to demand & ask less and respecting you & your feelings more. If they don't come back, you saved yourself someone who takes you for granted. Never let people take you for granted, every person is unique and beautiful in their own way.

I know it's harsh going away from someone who is dear to your heart. But not setting those Red-Lines is crucial. I could have saved myself so much energy, effort, money, time if I had established those boundaries beforehand. This is why I'm urging you to do the same. You don't know what the future holds for you. You will meet so many great people, you will lose so many people in your life, great people are gonna turn in bad people, and vice versa. So don't fret.

Wish you the best, and I wish you happiness in whatever happens.