If you are looking for a first hand account, you can read The Men with the Pink Triangle by Heinz Heger. It is the biography of a gay Austrian who is taken into custody and placed in a number of concentration camps.

Unfortunately, there are not many accounts, either biographical or historical, of homosexuals under Nazi rule. This is primarily because of the continued illegality of homosexuality in post-war Europe and because of the stigma that remained attached for many years after the war.

I have addressed the treatment of homosexuals in Germany and its occupied territories here. /u/commiespaceinvader has discussed the treatment of homosexuals immediately following WWII here and I have done the same here.

However, to give you a brief answer before you, I hope, go read the above book:

Homosexuals in Germany and its territories, although the Germans seemed to be less interested in homosexuality outside the Greater German Reich, were primarily brought in on criminal charges. It seems that they were, in many cases, released. However, repeat offenders, those seen as too overt, or those to whom the court took offense would be sent to concentration camps as degenerates.

The Nazis categorized camp prisoners using colors and triangles sewn onto the camp garb. In the case of homosexuals, it is the pink triangle, that signified one's cause of internment. While there tended not to be an "official" hierarchy in camps, there was most certainly an unofficial one and gay men were at or near the bottom.

Gay men were often beaten by other prisoners and were forced into sexual arrangements as those interned as criminals (red triangles) used them for their own gratification. Sometimes, a gay man could find a powerful kapo who would then become his protector, in exchange for sexual favors. Interestingly, although the criminals would force the gay men into sexual acts, they did not see themselves as gay and still punished the gay men for being "degenerate." Not really surprising, but it points toward different motivations for sexual activity and different perspectives on homosexuality.

Since gays were low on the camp hierarchy, they tended to receive less food, fewer "good" jobs, and more negative attention. This led to a higher mortality rate in homosexual prisoners than in the general camp population (we think).

This lead us to the "we think." Information is very hard to come by for the above mentioned reasons. Additionally, while we do have records, they are not complete and so we don't always know when a prisoner was released or even re-incarcerated. Hence, the number of homosexuals interned in concentration camps is unknown. Rüdiger Lautmann estimated the number killed at roughly 3-6 thousand while others have suggested 10-15 thousand. While some will state hundreds of thousands, this is far afield and not based on any academic work IMO.

Sources:

Lautmann, Rüdiger . “The Pink Triangle: The Persecution of Homosexual Males in Concentration Camps in Nazi Germany.” Journal of Homosexuality 6, no ½ (Fall/Winter 1980/1981):L 141-160.