Sexuality is not a choice. You can choose to act on it, sure. But not what you feel. Not who you're attracted to. Or not attracted to.
Lesbians don't need "a good fuck by a man" to become straight. If anything, that's just a recipe to prove to them how not heterosexual they are. Same in reverse with gay guys. Sex with a girl will not "cure" them.
Asexual people will not suddenly develop an interest in sex just because they have it. It doesn't matter if it's from the best lover in the world. Nor does--and this one may surprise you--being asexual mean a lack of libido. It can. But what it means is a lack of sexual attraction.
Sexuality is a spectrum. It's not Straight and Gay. It's heterosexual, homosexual, bisexual, pansexual, asexual and levels of each. Then there's romanticism--it's a spectrum, to. A person can be romantically attracted to someone without sexual attraction. And someone can be sexually attracted to a gender/multiple genders without experiencing romantic attraction.
These are not mental issues. These are the broad spectrum of humanity. Of love and sex and all of that. It is not caused by abuse (it can be exacerbated by it). It is not "cured" by further abuse. It is not your place to judge, condemn, diagnose or attempt to "save" or convert (sexually) people of a different orientation.
Acceptance, not 'tolerance,' is what this world needs. Love. Not conditional, based on what you are comfortable understanding. It's okay not to understand. It's okay to ask questions, as long as it's not in a derogatory way. It's okay to feel weird until you know more. It's okay to not know, and to learn. It's okay to be Takei, gay, straight, bi, pan, asexual or anything in between.
This is nature, how we were designed. Homosexual behavior has been observed in close to 1,500 species. It is real, it is as natural as heterosexuality--it's just less common.
So please, don't just 'tolerate' your friends and family of a different orientation. Love them. Accept them. Defend them against fools who refuse to learn or think. Be the change that this world so strongly needs.
And congratulations to the UK for taking the next step in this process!