to clarify; Do homosexuals hide their sexual and emotional orientation, or do they not only hide their sexual relations, but rather a large part of their lives, which reinforces feelings of loneliness and isolation.
Depending on the country and culture, a large number of gay, lesbian and bisexual people hide their feelings and sexual relations due to fear of exclusion or punishment. This is of course worse in countries where homosexual relations are penalized.
Your question also seems to distinguish between sexual attraction and "a larhge part of their lives". This depends on how important having a partner and sexuality is for people. Most research shows that having an enriching relationship is one of the most important pillars or the quality of life. When people are missing this, or when their meaningful relationship is shunned by society, considerable damage is done to their entire life.
In some countries, sexual life and having a homosexual relationship is accepted and can be part of your public identity, just like heterosexual relationships (marriage) are closely tied to social status and family support. In other countries where homosexuality in criminalized, having a homosexual relationship or admitting a gay, lesbian of bisexual identity may be shunned or more strongly rejected. For example, in Iraq, admitting to be homosexual or even being suspected of having a preference for one's own sex can (and is) lead(ing) to persecution and murder without intervention of authorities.
Homosexually attracted people in such countries face an unsolvable dilemma. Either they come-out and they will be victims of persecution and exlusion, or they don't come-out and sugffer the psychological damage of having to hide their orientation at every step, even going as far as beng forced to marry heterosexually, often resultang in a sexless of more generally unhappy marriage.