The answer's an uncomfortable one i'm afraid - you may never know. It's how you deal with the uncertainty or to put it a better way, how you work with what you do know.

So you don't feel sexual attraction - not that uncommon and plenty of people feel the same if you know where to look for them. Try this sort of relationship if you can and see how it fits, don't be surprised if your feelings change depend on who you are with. This is normal. On the other hand they may not and you may feel closer to answering your question. Again, normal.

I guess you can only keep exploring and come to know more about yourself as and when it happens - there are many schools of thought when it comes to sexuality but it's about what works for YOU. Don't forget that.