Was I molested?

Hey my nick name is Anna. Okay I'm almost 16 and I keep having these memories of being "touched". 
Okay so back ground when I was about 8 my parents got divorced and a year later my dad remarried and my step mom had 4 kids. Two of those kids were twin boys that are five years older than me named Chad and Jeff.  I also have a little brother that's 2 1/2 years younger than me named Poe.  So flash forward a couple years I'm 9-11 and in 4th or 5th grade. Chad and Jeff are 16 because I remember them driving. I went to my dads house for the weekend and that's were it started. 
So I'm almost positive this only happened once. Me, Po, Jeff, and Chad are having a tickle fight and they are throwing me and my younger brother on the bed and we're all having fun and laughing. The suddenly Chad kinda got be and layed me on the bed. I remember Chad telling me it's okay and to like open my legs and he rubbed my clitoris for a sec and I had no idea what was going on. And he kept telling me "it'll just tickle" or something like that. It only lasted maybe 10-15 seconds. Then everyone just stopped and went to watch tv or something. 
I don't remember where my parents were but I do remember a couple other things that happened later on. 
I remember Chad and like 2 of his friends were in the kitchen and no one else was home and I walked in and Chads penis was out. I don't know why I just remember awkwardly leaving. 
So about a year after that happened I was in 6th grade (so age 12) and started watching pornography. My mom later found out and so I stopped. 
About a year after that in 7th grade I started masturbating. I don't remember how I started watching porn or masturbating. I don't know if it has anything to do with the incident. I'd say I masturbated quite a bit like at least once a day when I started. Also from 5th grade to about 8th grade I had some depression 
I'm almost it's been 4 or 5 years. It hasn't happened again that I remember. I've been suppressing these memories for so long and just writing about them for the first time I can't think about what happened. 
He's 20 now. He's been nice to me. He has a job and a life. He has protected me when me and my brother get in fist fights. I don't know what to do. I don't want to ruin his life. 
I don't feel comfortable telling anyone just yet. I guess I have some questions. 
1) Was that even considered molestation?  He was 16 and I was 11. It wasn't consensual but I didn't say no, because I wasn't sure what was going on. And it only happened once. 
2) Is the porn, masturbation, or depression related in any way? 
3) What can I do about this ?? 
4) Whould any one besides my mom and dad believe me?I have no evidence and it's been so long. 
5) Is doing something worth loseing my whole family? My step sisters wouldn't want to believe me. Jeff my other step brother and Poe were there. Jeff was 16 and Poe was 8 ish. Do they even remember and would Jeff testify against his twin brother? Would my step mom still love me? 
6) Is these even a big deal
I can't stand to proof read this I'm so sorry if there are any mistakes.