Thanks for your question and please forgive the long wait for this answer. You're curious as to whether it's possible for sexual abuse to make someone gay. The short answer to this question is no. There is never a single root cause to someone being gay.
There are indeed cases where people who were sexually abused as a child will either attempt to seek out sexual relationships similar to the abuse or avoid sexual relationships which may remind them of the abuse. In your case, you are clearly attracted to girls. The sexual trauma you suffered may have caused you to avoid dating boys but it couldn't have created an attraction to girls that wasn't already there
I of course have no knowledge of the sort of counseling (if any) you've received to help you recover from your abuse. If you are concerned that these events in your childhood have caused you to avoid seeking romance with boys that you otherwise would have been interested in, you may want to discuss this with a therapist.
Just try to keep in mind that liking girls, or girls and boys is normal and there's nothing wrong with you for having same sex attractions. Thinking that it in some way is the cause of early life sexual trauma can lead to feeling like you're behavior is a sort of negative symptom. This simply isn't the case.
There's an article I found which goes into detail on the subject of your question. It may be of further help. It can be found at this link: http://www.kalimunro.com/article_gay_abuse.html
Good luck, be well and please don't hesitate to contact us back with any further question you may have.
Philip for AlterHéros