Help please - My Son's Father is in a relationship with a woman who does not want him to have a relationship with our son

I'm sorry for the long post, this is my first and I don't know how much I should say for anyone to understand the situation from the outside.We dated in highschool. Got together 2 years after highschool. I got pregnant, and we had our babies premature. A month later our first born twin passes away. I lost it, and we went through a very rough time. We pulled through for our other son, and gained a very close friend ship.We decided to bring our son to his childhood home with his mother, and grandma with Alzheimers. So I can have help raising our son, and his mom can have help with his grandma. He soon starts a relationship with the other woman, and she does not trust him. He became very angry, and aggressive towards both of us. We would go through fights, and then be friends.Before my son turned one, his father started a job out of town. He was gone for months at a time, and was pretty much gone all of last year. After that he moved in with the woman in February, and got a closer job. He promised to come visit, and to help financially. After that he told me that his girlfriend did not like me, so he could not have a relationship with our son. He wasn't there for his birthday, for 3 separate medical emergencies, and ignored any text or call I sent.In August he moved back in to take care of his grandma who was on hospice. He broke up with girlfriend, because he said he was tired of being controlled. Things where good between us, with the three of us living together peacefully. After his grandma died, he went through a destructive faze. And ultimately got back together with girlfriend. Now he is being an ass to me, and almost completely ignoring our son. He went through the trouble of establishing his trust, and creating a father-son relationship with him. My son doesn't understand why his dad is being like this, but it hurts me to see him try to see him get hurt. He loves his dad, and he looks up to him. I want to do something, but I end up saying the wrong things. I don't know how to deal with this side of him, its like he's a completely different person.I don't know what to do, and I don't know if there's anything I CAN do.Has anybody had a situation like this? If so, what did you do? via /r/Parenting http://ift.tt/2xangBL