Heart broken 💔

I was with my ex for 5 going on 6 years this year. We've been together since 16 and 18 now were 23 and 25. This year we found out we are having our 4th child together, we ended up spliting up in march so been separated for 7 months almost. Hes already in a full blown relationship with a girl that caused a problem way before we split and he used to tell me im jealous of her etc when in reality i knew what type of woman she was and i knew she wanted him. I have our kids 24/7 he only gets them every other weekend. I dont understand how you can go through so much with someone and they up and walk out on their family for someone else and give that person everything you wanted from them. I never cheated when he cheated a million times and i forgave him and i delt with so much and this woman will not have to go through have the stuff he put me through. I cry alot because its not fair to do anyone who really loved you like he did me and i put so much stress on myself and baby cause i just dont understand how could someone do me like that. He dont care at all anymore to point he's a complete ass to me and its hard like i just wish i could hurry up and be happy as fast as he was.