By all the posts above, I am sure you would have confirmed your doubts by now, regarding your childhood abuse and now looking at remedial measures to be taken, before you embark on a new journey of life - marriage. My best wishes for that, you deserve all the happiness and joy.
Let me add that mine start similarly though with a boy same age and also an elder man. Both compounded the affects of each other, and later it all snowballed into abusive episodes with both.
Even exposure to porn as a child can have an equally devastating effecting effect on a child's mind.
Anytime a child is exposed to a sexual experience or feeling before he is ready to do so can be considered an abuse of his right to choose as he didn't get to choose, even though it might have felt normal or appropriate and even consensual at that time. It is abuse of our freewill, all right. That is why, most abuse victims have an issue with saying No, because once they couldn't and hence take the entire life time learning when to say no, and when to say yes as well. That is the flip side of the problem we take so much power from denial of others and ourselves that we often forget to say yes to the right situation and people, who enter into our lives as healing agents and simple agents of change.
BY the way, the timing for this revelation is so appropriate, as now you would enter in this new phase of your life with greater awareness, and healed.