Al-jawab billahi at-taufeeq (the answer with Allah's guidance)
homosexual relationship is totally prohibited in Islam.
Islam considers homosexuality as a sexual deviation leading to a perverted act which goes against the natural order Allah intended for mankind. It is a corruption of the man’s sexuality and a crime against the opposite sex. Therefore, the Islamic shariah strictly prohibits the practice of this perverted act. This is mentioned in many places in the holy Qur’an.
The story of the people of the prophet Lut who were addicted to this practice, is the best example.
Allah Ta'ala says,
Prophet Lut (‘Alayhis-salâm) said to his people: “Verily, you do sodomy with men, and rob the wayfarer! And practice all wickedness in your meetings,” (Al-Ankabut, 29:29).
And he said to them: “Of all the creatures of the world, will you approach males, and leave those whom Allâh has created for you to be your wives? Nay, you are a trespassing people!” (Al-Shu‘ara’, 26:165-166)
But their answer to Prophet Lut (‘Alayhis-salam) was: “Bring us the Wrath of Allah if you are telling us the Truth.” (Al-Ankabut, 29:29). And so Allah gave them the punishment they deserved: “And We rained on them a rain of torment. And how evil was the rain of those who had been warned.” (Al-Shu‘ara’, 26:173).
Sayyiduna Abdullah bin Abbas and Sayyiduna Abu Hurairah (RA) report from Rasulullah [Sallallahu-Alayhi-Wasallam]:
"Accursed is he who commits the act of the nation of Loot (Alayhimus-Salaam)." - Mishkaat p.313.
For more information please view this article by Mufti Zubir Bayat: http://www.direct.za.org/articles/Social/homosex/homosex.html
If a person who has made homosexual to be allowed then he has indeed commited Kufr (disbelief).
This type of Kufr, is Kufrul-Istihaal which falls in Kufr Akbar (major disbelief).
Kufrul-Istihaal: Disbelief out of trying to make Haram into Halal, vice versa. This applies to someone who accepts as lawful (Halal) that which Allaah has made unlawful (Haram) like alcohol, adultery, homosexual etc. Only Allaah Ta'ala has the prerogative to make things Halal and Haram and those who seek to interfere with His right are like rivals to Him and therefore fall outside the boundaries of faith.
A person who has commited such an act but doesn't make it allowed then he is a Faasiq (transgressor).
One should repent at once.
As Allaah Ta'ala says : "Say: 'O My slaves who have transgressed against themselves (by committing evil deeds and sins! Despair not of the mercy of Allaah; verily, Allaah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful'. [39:53].
In another place Allah Ta'ala says, "Ask your Lord for forgiveness and then turn in repentance to Him," (11:3) and He says, "O you who believe! Turn in sincere repentance to Allah." (66:8)
Rasulullah (Sallallahu Alaihe Wasallam) said,"The one who repents from sin is like the one who never sinned." [Ibn Maja (3240)]
Prophet (Sallallahu Alaihe Wasallam) said: "Islam (i.e. converting to Islam) wipes out all the previous (misdeeds)" [Reported by Imam Muslim ].
He also said, "Remorse is repentance." [Ibn Maja (4242) and Ahmad (3387)]
Please view this link for more information and advice: http://www.muftisays.com/qa.php?viewpage=viewQA&question=3568
And Only Allah Ta'ala Knows Best.