I understand how you must be feeling but you have to look at this from his perspective.
His father was done for harassment which wouldn't have happened if he had gone through the proper channels and then abandoned him by still not then going through the proper channels.
His mum lost him age 8 because she was abusive.
He's had no family for all this time.
You suddenly pop up on Facebook and want to have a relationship...
I'm afraid he doesn't know you and he doesn't automatically have feelings for you because you are family. Look at all the ways he has learnt that family lets him down.
He has your contact details. Let him come to you if he wants to. Until then you have to respect his wishes.
Maybe you should get some counselling to help you cope with this.
Fruit flies - help needed please.
Army horses loose on London streets
Have any of you got all electric cars? Pros and cons please.