PLEASE HELP - Did I sexually abuse my brother?

I am 22 year old woman and my brother is 17. We are 5 years apart.
Growing up in my teens, this didn't bother me at all in fact I don't even think I remembered it.
As I have gotten older, I am starting to get flashbacks from when I was younger. I can not remember a lot and I don't know if this is because I have blocked it out or it was just so long ago.
I think I would have been about 11 as I was still in primary school so my brother would have maybe been 6 or 7. The only instance that I remember with actual circumstance was being at my grandmothers where we went in the holidays sometimes. We explored each other by touching and I remember being interested in the fact that my brothers penis would become somewhat erect (because I had no idea what erections were). I don't know how it started, or how it ended but I know that there was times that he would actually initiate things and I would say yes or no. It was generally just rubbing and touching. I am feeling so much guilt and shame as I am studying at university and I suffer from anxiety and depression where I have attempted suicide once but am now thinking that this could be one of the causes of my pain.
There is no indication that my brother remembers it, he has had a happy childhood and has friends. He games a lot but he still does well at school and plays sports. We don't talk a lot as we live away from each other now but we do still see each other a few times a year and laugh and fight as siblings do, it is a pretty normal relationship. But I am wondering if he remembers and if he hates me for it?
I am too frightened to ask him in case it brings up memories and creates awkwardness and tension between us that might actually be unnecessary.
Other than battling depression, I have had a pretty normal life and still find moments of happiness and I have healthy relationships with friends and I don't have any issues in around sex with people.
Sometimes this just jumps into my head and I found it so difficult to even find this forum, with all of the support being on the victims (which I totally understand) but I feel so sick.
At the time I didn't even know what sex was, or what we were really doing and I have no vivid memories but I know it happened.
I'm worried that this is going to hang over me for the rest of my life, and telling future partners about what I have done.
Did I sexually abuse my brother?
What do I do?
I can't live with the guilt.

I honestly doubt what you did would be considered sexual abuse as you were a child, and probably did not know the full extent of what could result from actions. You were a child when you did this, and are nowhere near the same person you were back then, physically, mentally, or emotionally. I suggest you check out Sprocks You are not all Josh Duggar thread, as I think that it fits your situation perfectly. To sum up the thread, you would not judge a child the same way you would an adult, and you would certainly not call a child a horrible person or a monster if they did something similar to what you did, so you really shouldn't be that hard on yourself. You've obviously reflected a lot on this, and you know that it was wrong, so I really see no reason for you to continue feeling guilty over something you did as a kid. You're not a bad person. Your past does not define who you are, especially what you did as a kid, so please try not to be too hard on yourself.

Yes, please do check out my 'You Are Not Josh Duggar' thread - probably one of the most important I've made on here in terms of applying to quite a lot of people who post here.

Great response, FLaM and seconded

I think that as kids, we have a natural and innocent curiosity about our bodies. We only learn about 'good' and 'bad' touching later.
We are capable of arousal early on. It may form an imprint of how we go about things in later life.
I remember playing 'doctor' and 'house', doing the things that parents might do. It was growing up and learning. Taking off clothes in a safe setting is things that kids do.
Why we might remember it at times later in our lives, I don't know. Try not to let it trigger guilt or shame. If he is seemingly OK with it, you should be as well.
It wasn't being abusive, cruel, sadistic or perverted. It was 'play'. I think that most all of us go through this.