My blended family disaster HELP! PLEASE

Hi guys, I need help or to be honest I have no idea what I need… On Thursday my relationship with my partner ended. The reason being is despite my cry’s of help or trying to reason with him as nicely as I could my partners 5 year old son would badly bully my 4 year old son… I tried to talk, have conversations with him, try come to some sort of conclusion to fix this… the thing is that on my side of the family my son doesn’t have anyone his age he is the youngest of all his cousin. Where as on his side, his son had multiple cousins his age and when they got together it was really really bad. To the point of my son was asleep I walked into the room and his son was dangling a big hard suitcase over my son’s head about to throw it on him. I just lost it and told his father this isn’t right! Your son’s behaviour is not normal I think he needs help! I begged him please help me fix this situation! The father blamed my son said it’s just boys being boys… What the??? So I took my kids packed up and left. It’s my job to keep my kids safe so I took him out of the situation. My son is a very kind caring kid. In my own heart I wish I raised him a little bit more harder to deal with these situations but on the other hand why the hell should I have to! I have two other kids also, older girls who were tired of it and we’re happy to leave also. Now I know I’ve made the right decision getting my kids out of there. I know that. But I guess what I need help with is why the hell does it hurt so much. He knew what I went through with my kids father… It was hell… I had built walls so damn high not even king kong could’ve smashed them down but he was so persistent for a good year that eventually I introduced him to my kids and those walls crumbled. A week ago he held me in his arms crying saying he’d never known true love until he found me and now I’m just the scum of the earth… I’m not right in the head at the moment … how can someone just do that… Take your heart and completely stomp all over it… My kids have to come first and always will. I just wanna stop feeling heart broken and I feel like I sound really stupid. I don’t have any close friends but my parents are really supportive. A week ago we had the picture perfect relationship… I feel like a complete failure. Like I’m not good enough for absolutely anybody…or anything… I’m sorry for going on. Hopefully someone has some good advice for me :pensive: thankyou…