It depends on how abuse is defined; I think with kids there has to be more than 3 years difference or it's just "experiment" or whatever they call it and neither party is responsible for any negative feelings. In some ways it certainly sounds traumatic though, and I wouldn't be surprised if someone suggested you had PTSD from the whole experience from the beginning through the teasing and all. Since he was a child too and "slow" as you put it and experienced the same teasing, I think it was just a really bad experience for both of you, influencing you now. But there wasn't an adult you had to obey or anything which is usually the way abuse is defined. I fooled around with cousins and girlfriends, etc. and am ashamed of that and influenced by that but that wasn't abuse, just one's whole makeup and experiences and background teaching, etc. not meshing together well.