Some cases of homosexuality / lesbianism / transexualism, arises
because the individual soul had incarnated in so many lifetimes as
that paricular sex / gender, that the soul energy becomes
predominantly either masculine or feminine (and there's nothing
wrong or 'sinful' about that, it's a matter of personal free will
and choice), that it could present various difficulties adjusting
when incarnating into a physical body of the opposite sex /
gender.
Other cases, however, could be a result of the soul needing /
intending, for various karmic reasons and learning purposes, to
incarnate into a physical body whose genetics and/or probable early
life experiences, would predispose that incarnation towards
homosexuality / lesbianism / transexualism. This could well be
related to, for instance, if a soul needed / intended the
experience of being discriminated against by society (eg. a
severely imbalanced racist might choose to incarnate in the next
lifetime as a member of the race he discriminated against, to
experience and understand both sides; karma is not about
punishment, it's about learning), or for the purpose of developing
personal strength (eg. to accept oneself even if society doesn't
accept you), etc.
In any case, homosexuality / lesbianism / transexualism, is not
regarded by the guides & helpers as anything 'sinful' (morality
is a human illlusion in any case), but rather as a karmic
experience, opportunity and choice (either for accepting it, or for
declining it; either is fine, there is no right or wrong, it is the
personal choice that matters).
While some are hardcore cases due to the overwhelming influence
of biological genetics, soul energy or soul karma; there are also
many cases (it's a spectrum really) in which the incarnated
individual does have the free will (and in many cases, still does
to this very moment) during incarnation to choose between
heterosexuality / heterosexualism, or to choose homosexuality /
lesbianism, or to choose transexualism / transvestitism.
Again we reiterate : there is no right or wrong, no such thing
as 'sin', either choice you choose is fine, because it's your
choice. It matters more than you can accept, respect and love
yourself, for whatever you choose for yourself.