When a mother misses..

I've been checking on some of my friends Facebook account and saw one notification. One of my friends celebrated friendship with my son. I fell silent. It's been almost 3 months since my son left and went to his dad's. I think he is decided in staying there for good. 
I am in tears. Last time I felt this pain was when one of my sons died. 
All these years I've faced challenges that many would admire me for being strong. Brave. What they don't know is I am always terrified. 
I am afraid of being alone. I fight because I know I have my children with me. I am strong because I know I have them. But now that I lost another one, it is somewhat devastating. 
Him being with his abusive father makes it even worse. 
I know my ex uses this as an advantage against me. He uses this to make even. 
This is the only way he can hurt me again. I can only imagine that smirk on his face. Thinking he has won. 
I miss my son. I miss him so much. It is so hard for me to go on with my everyday life having this hole inside of me getting bigger by the day. 
I would always pray that he misses his mom as well. 
That somehow he would even talk to me. I really couldn't understand. We never have any argument or misunderstanding. 
He just had a fight with his sister and he decided to leave. He decided to stay with his dad instead. 
I never had a say on it. Suddenly it felt as if I lost my right to be his mother. 
I feel useless. I feel like I'm not good enough.
I still have 4 of my kids with me but it doesn't feel the same. 
My heart will always ache for the sons I have lost. 
Somehow I still manage to keep the fight. But it's the hardest thing ever, to go on every day knowing you already lost 2 of the most important person in your lifetime.