Hi Carolina
I too was the victim of sexual abuse, when I was a kid and I never told anyone, until I was in my 30's, I was given the phone # of a PTSD therapist and slowly over time, I was able to deal with and put it away,
You stepfather has a problem, and it was very wrong of him to do that to you and your sisters, YOU ARE NOT AT FAULT!!! you did nothing but love him like a dad and for him to do what he did is horrible, it set you on a course for your life that made you different from everyone else.
I felt that way my whole life, and I hated it, I was starting not to want to drive anywhere, afraid that I was in other drivers way, I was withdrawing, using recreational drugs, drinking, living a bad life, and I hated it, but that was all that I knew.
I can tell you that I have dealt with my PTSD and what I have received back it an entire new life, then in Dec 2004 I was diagnosed with Multiple Sclerosis and if I had not worked thru all my pain, then the MS would have swallowed me whole and I would not be were I am now. I realized also that I have had depression my whole life and I like you would put on a happy face

and be positive and happy and it was all apart of my mask that I wore. Now I am happy, relaxed, confident, content, and this is the life that I earned from all my pain.
Talking about it will make you feel better, finding a PTSD therapist who can work with you to really put it all to rest, may be the key to your new life. I went to a Psych and I spilled my guts to him and he presctibed a drug to handle my problems, yeah, I never went back to him and it made me shy away from any sort of therapy, but after finding my therapist, it was the best thing I ever did.
I like to let my brain sort things out for me while I sleep and maybe that will work for you. I will give you any support to help you feel better.
I love nitros advice, get it out if you want to do it here and it helps we will listen but it is apart of your life, and it wants to get out, you want to reclaim you. Hang in there sweetie, things will get better