Gay,Bi to Straight?
Yes ... There a certain amount of programming... Reach beyond that and anything is possible
Gay folk fought hard to win the nature/nurture battle. If what you suggest is true, then all was for naught.
Anything is possible with the ability of the mind to WANT it badly enough. If I am gay and I want to be straight, maybe I am straight, deep down. Who knows? Who cares besides the person who is questioning it? Again, anything is possible. You do have to carefully examine how you think and feel.
Some people say that our place on the sexuality spectrum fluctuates over time. I think it's plausible.
There is a scale. I would argue we all fall on it. Identity may take years to determine, or may never be discovered at all. I identify as gay. Others may identify as bi, while others may identify as straight or none of the above.
I think you discover more about yourself as you get older. When you're younger it is okay to question who you are. Hell, even when you get older. You only live once, as they say.