I believe that one can change, just as everything else in the universe can change. As a rock can seem stagnant in time, it also changes through erosion by being eroded or can be combined with others to become a larger rock. I'm not saying a gay man can all of a sudden become straight, but can meet a girl he is attracted to and possibly become bi. Or a man can obtain a foot fetish , or the like, through different sexual activities through the his life. Though if one views their own sexuality as a fixed construct, then it probably is. We are all different and see ourselves as such. So a person who dosnt have such fixed feelings about themselves can change who they are. So if I'm a male who only likes sex between a man and a woman and believes that this is the only good type of sexuality, I'm more than likely not going to ever want to try male on male sexua and will be fixed in my sexuality. On the other hand if I was a male who only had sex with women, though was more open to new sexual opportunities, I may learn from the right male to appreciate and enjoy gay sex. One could say that this male was always bi but was in denile, but some could also say that gays are bi but also in denile. I personally believe that these labels fix people into certain categories making individuals less likely to stray into others, but not many actually fit 100%. just as not all women fit into the gender category of what a woman is, as some enjoy dressing more like men, wish to be men, or just wish to be themselves. Again I don't believe one can become 100% straight from being 100% gay overnight, but as a decorator crab changes its appearance through acquiring different objects, a person can also change itself through different life experiences if they are open to the possibility.