...mh, I don't think it's strictly a matter of straight or not, rather, to give the deputed hero a love story no matter what.
to make him more complete... could be.. :(

First thing that popped into my mind reading this was Hellboy movie, in wich there is a love story between Hellboy and another important character of the support cast that, AFAIK from what a friend that actually read it told me, in his comic canon has something like a history with another male support character.
I'm sure there are other examples around..