That's the difficult part and it is multi-faceted. Being sexually abused by an older male oftentimes leaves the victim wondering if he is gay. This comes from the fact that the body reacted to the sex, the victim became aroused. In many cases the sexual abuse was the victim's first exposure to sex, again instilling the idea (fear?) that he might be gay. I know many survivors will agree that the physical part felt good (it hurts to say that, to admit that). Of course there are others who experienced physical pain and violence during their abuse and that would manifest in its own way. But for those whose bodies reacted, for lack of a better term, positively, it leaves many questions.
Your question with respect to: Why would anyone ever want to have sex with an older male if that was who abused you (I'm paraphrasing) is complex and cannot be answered easily. I don't think 'straight'victims want sex with a male but they are looking for answers. They are looking, as I stated previously, to regain some of the control that was taken from them. They are seeking to 'relive' the experience but on their terms, again in an effort to regain control. These, and other ways of acting out, are common reactions to CSA. Many of us share them, none of us planned it that way or wanted it that way but many of us didn't/don't have the tools to know what is happening while it is happening or how to stop it from happening. No one wants to act out this way, just as no one sets out to be a drug addict or alcoholic. There are things in our past that seem to lead us, to control us, compulsions that seem like they won't stop nagging at us until we act them out. Personally, once I understood what it was that I was doing, that I was in a sense perpetuating the abuse, I was able to stop. Sometimes the desire is still there, sometimes it is very strong but if I think about it and what the end result will be (guilt, disgust, shame, pain, regret, emptiness, questions still unanswered, just to name a few) I can make the desire go away, usually. Or I can at least decide that I am not going to act on the impulse if I know how I'll feel afterward.
I can truly say that, regardless of the type of committed relationship I may have been in at any given time, my actions never had anything to do with the other person. I felt guilty that I had betrayed someone I cared about, but I always felt that I had no choice in the matter. Now I know better because I have learned about what I was doing and why. I hope this helps to make more sense from my previous post.