User blog comment:OmegaSpruz/The Romance Stuff/@comment-730941-20100720004216

It is very complicated. I did see one mod being worked on that allowed players to romance same-gendered characters, but it was never finished.

Doing the same thing in the first Mass Effect was relatively easier, check out this thread here: http://social.bioware.com/forum/1/topic/104/index/2771955

But I haven't found any easy way of romancing same-gender characters in ME2 unless you're a modder yourself and know what you're doing.