I don't understand how anyone can confuse sexuality as I don't feel there is much thought process involved, you just feel what you feel and that's all there is to it.

I don't think the lines between gay, straight, pedophile, etc. are as clear cut as we sometimes are led to believe. We give sexual orientation simple titles because it is easier for us to categorize people in that way; but I believe if I were to be truly accurate when someone asked me my sexual orientation, I would have to respond something along the lines of: "75% homosexual and 25% heterosexual on the male/female scale and 90% pedosexual on the age scale with a focus on the 8-12 range and a preference for petite body types". Thus I think it is understandable that for someone on the far side of the scale, confusion is unlikely to ever occur. But for someone who is not as far as on the scale as you are, it can take time to figure out exactly what it is they are into.

how does being molested cause anyone to abandon their original determined sexuality from birth, what happens to their original sexuality when they become pedophiles?

What I have run into is people whose early sexual encounters caused them to acquire additional sexual interests. I am not familiar with any cases where a sexual encounter appears to have completely changed the person's sexual orientation.

If being abused caused them to become pedophiles then how does this relate to the research and study claiming pedophiles have a detectable difference in brain matter or they are slightly shorter in average length, does this mean that pedophilia can be caused by two different reasons, biologically or due to abuse?

Such research is in its infancy and should be taken with a grain of salt. Not only that, but such research, out of necessity, is focused on the study of prison populations and quite often fails to take into account the inherent differences between situational and preferential pedophiles. Thus, the existing research at this point in time is practically useless.

Having said that, there is little doubt that like so many other personality traits, there is both a biological and environmental factor involved. Take alcoholism for example. There is research showing that there is likely a genetic factor to alcoholism. Yet, the fact you have the alcoholism genes is irrelevant if you never have a drink to begin with. Your genetics may predispose you to having a drinking problem should you ever choose to drink, but unless you do those genes will never show their effects in your life.

...does this mean only children are susceptible to altered sexuality?

All people are capable of adapting sexually. If you study prison populations, pre-industrial maritime culture, and other situations where men are forced by circumstances into living for extended periods in the absence of women, you will almost always discover that homosexual acts were (or are) commonplace in such environments and that in fact the people participating in such acts do develop attraction towards individuals that outside of those conditions they never would have been attracted to. Rarely do such individuals "switch sides", they just add other sexual attractions to the ones they already had. As a former inmate who had had one too many drinks once told me in regards to that phenomenon "when there's no bread, you have to eat crackers".

If being abused lead to pedophilia then why does this not apply to every child who was abused sexually ?

If cigarettes cause cancer why doesn't everyone who smoke get cancer?

It's not that cigarettes will cause cancer every single time. It's that cigarettes increase the risk you might get cancer. Likewise, I don't believe that anyone is claiming sexual abuse will cause pedophilia every time, but rather that sexual abuse increases the risks of becoming a pedophile.

Having said all of the above, I have to admit that I am a skeptic about the link between sexual abuse and pedophilia. Having known so many BLs over the years, I have seen very little evidence that there is any greater incidence of past sexual abuse within the bl population than in the population at large. In fact, we once did a survey on this forum and discovered that our members are no more likely to have been subjected to sexual contacts with adults as a child than people in the general population are. I personally believe the evidence isn't there to support a claim that early sexual contacts with adults increases the chances of becoming a pedophile. I believe the evidence that exists is flawed based on failing to differentiate between situational and preferential pedophiles and using prison populations exclusively.