Blast from the past!

I'm sitting here at work this morning when I get a message on facebook from a step sister that I have never met.
Let me give you a little back ground before I continue:
When I was 12 my father went to the states to meet up with a lady he met over the internet, he came back and told us that she and her six children were moving over here to be one big family with us. My brothers and I were excited at the prospect of having 9 kids in the house, we went house hunting with my father and found a huge house with acreage and the best tree house I had ever seen in my 12yrs, he told us we were going to all live here...it was like all my christmas' had come at once. I could not have been happier.
Fast forward to 3 months later, my father left for the states to bring 'our new family' home and never returned. So many broken promises of coming to see us and a few empty phone calls a couple of times a year....he never did come back and after the 3rd year of him being gone my brothers only just started to realise that he wasnt coming home.

I have been filled with so much hurt and anger for the past nine yrs and am still battling with my demons everday. Without anything been said I blamed my father and have gotten use to his parents feeling bad for us and sending us christmas and birthday presents saying they were from him. Why did he always promise to come back for a visit and never did? He missed my graduation, 18th, wedding and just recently my 21st. Now my brothers have to go through all those missed milestones as I did and I feel bad. He has a grandkid on the way that he won't even get to know (hopefully there will be 2).

I received a msg from Ali saying how sorry she was for everything and if she could change it all she would. She also told me that I shouldn't be angry at my father as everything is not what it seems. I really had no idea what she was going on about so after talking to her for a few minutes I asked her to elaborate. Apparently my father saved up so many times to come back but his 'wife' (and I use that term loosely) had a spending problem and took all his money. She controlled him and her kids so Ali left (she is 17 now). She lied about haveing cancer and many other illnesses and gave herself self inflicted injuries by popping pills to stuff her body up. The kids real father lived downstairs in their house and sexually abused the kids. WTF is wrong with this women? She told us that she adopted two of the kids she said where her nieces because ther mother was a drug addict and left them on her doorstep. I just found out that they werent her nieces and their mother wasnt her sister at all, they were foster kids that were there for only a few months. Ali doesnt even really remember who they are.
I feel like a huge weight is lifted of my shoulders..my father really did care, he tried to come home but she did everything to stop him. I also feel sad, that he is stuck over there trying his best to make a go of it...no real family but them. His whole family is here!
I really don't know whether I will see him again, I guess I have not really thought about it that much. If he does come back I don't know how I would react, I would feel like I was betraying my step-dad because he has looked after us and done everything for us all this time.
When we were kids he was a fun dad. He took us places and did things with us, mum never really had time for my brothers and I.
I really dont know if I still want him to come back after all these years.