After 8 years of relationship, we broke up and he’s getting married to someone else within few months.

I was tomboyish kind of a girl since start. I have always been a giving person. Never thought about myself but others, never lived for myself but others. I was happy in their happiness until I met a boy. I never believed in love, or dating or marriage as I had seen a lot of damaged relationships since childhood.
He came into my life, was my best friend for three years during college and then proposed me by the end which I accepted. I was attracted to him at start but eventually fell for him everyday. I loved him to such an extent that I lost myself in the journey. He gave me respect, love, care, his everything. He was everything for me. He promised marriage, we discussed after marriage life, children, I was there with him throughout for 8 long years. Now we are settled and doing good at our respective carriers. He’s in government sector and I work in leading private pharmaceutical company. I turned 27 recently, I had planned I will get married, settle down finally as that was the only goal I had in life.

He was trying to convince his family since last 2 years, his family was strictly against it. As our castes are different (subcastes rather, we are both OBC Hindu) Things went down to such an extent that when he finally said he’ll marry me or noone else his mother attempted suicide by drinking phenyl and was admitted for 2 days. He wasn’t even allowed to see her and was blamed throughout. After discharge, his mother threatened to repeat such thing again if she hears anything related to me and nobody would be able to save her then. To this suicidal threat, he agreed to marry a girl of his parents choice.
Now after a month of him agreeing, he’s going to get engaged and I am shattered into pieces. I’m feeling SUICIDAL. He promised me he would marry me on New years eve this year and I went crazy. I was dancing as I was that happy. The memories keeps coming.
I can’t breathe, I can’t eat, my chest pains everytime my head hurts my heart hurts I’m crying everytime dealing with panic attacks every now and then feeling like choked my eyes are swollen. I don’t know what to do. There’s no job satisfaction, my family is highly dysfunctional. We don’t talk about our personal lives, emotional talks. I’ve always been oversensitive and o eremotional. I feel everything is gone. I feel dying is the only answer. I don’t want to be part of such thing in this generation where family doesn’t care about their own child’s happiness. Yet again due to lack of education and stupid beliefs lives are ruined.
He’s speaking with that girl, now he has got someone to help him move on. His own which I believed was my place. I cannot imagine my existence without him being around. And that place giving to someone else? I would rather die than seeing that. I still wish if someone can make his family understand. I still wish everything gets sorted. I still wish everyday to see him.

What should I do?