I must say that I never heard that two men cannot be buried next to each other. That is normal practice in cemeteries. For example, in a row of graves they will not bury (assuming spouses) man, woman, man, woman, man, woman, etc but will bury woman, man, man, woman, woman, man, man, woman, etc. And except for being buried next to each other there is no declaration of them being spouses or whatnot. What is written on the gravestone is a private matter unrelated to the chevra kadisha and the selection of a plot for burial.

The LGBTQ community is raising a flag of victory of sorts. In Rishon Letzion they succeeded in getting what they consider recognition from the chevra kadisha, for the first time ever, for a homosexual couple to be considered married to be buried next to each other. 

A young man died of cancer, after battling it for a few years. His spouse wanted him to be buried with the adjacent plot reserved for himself as his spouse. They specifically had discussed the desire for Jewish burial, together as a couple but assumed the chevra kadisha would not allow it. They were prepared to go for civilian burial, if necessary, but explicitly preferred Jewish burial.

They were surprised the chevra kadisha allowed it, and had a full religious burial with kaddish and everything, and the adjacent plot is reserved for the spouse.

source: Mynet Rishon

I am happy they found peace and their grief was not turned into a religious battle, but I am also not sure what the big victory is. There is nothing wrong with two men being buried next to each other and it happens all the time. I am not sure on what grounds the chevra kadisha could have prevented it or refused the request, even if they did not like the optics.