In the movie, Mac seems to be the most affected one than anyone else when Blain is killed. They seem to share some strong connection.
Is there any chance they are gay or is it a very strong bond they formed over their intense military/mercenary experiences?
The film's official novelisation goes into a bit more detail about Mac and Blain's backstory. The very short answer is that both of them share a deep bond, but one of brotherhood of arms, not a sexual attraction.
“Good work, Sergeant,” Schaefer acknowledged curtly, his mind trying to process a hundred details. Then, suddenly sensitive to the bond that lay broken between Blain and Mac, he added softly, “I’m sorry, Bull. It’s never easy. He was a good man.”
“I never had no brother. He was it,” Mac replied simply, almost matter-of-factly, his lips tightened as if to contain his emotions.
