I have Legacy, but no details for same sex marriage. (Only this person had a relationship with...)
You do have a problem there, as the program has only male and female lines. What Legacy program is yours? Mine is 7.0, and there is nothing written in my book about same sex marriages.
The only other thing to do is contact legacy and ask them if any of their updated versions include same sex marriages.
I guess not a lot of people have came across this before, and I have a feeling Legacy has something to do with the Latter Day Saints, so this certainly will be a no go for them.
Regards
Suzy W