It was Murdock that he bonded to first. Murdock, the is-he-or-is-he-not-crazy pilot. While certainly not the first friend Face made in his life, he was nearly instantly the closest. They shared many commonalities - the most obvious one being the team, but beyond that, they shared the the loss of a mother. It wasn't something either of them discussed deeply, but when Face tested the waters with a "My mother left me when I was five," Murdock had simply nodded, blinked hard once or twice, and answered with a "My mom died when I was five. I know what it's like, muchacho." Then, without so much as a simple slap on the back, he went back to cleaning and reassembling his service weapon.
And just like that, the bond deepened. Little by little, it grew. If Face needed a partner in crime, it was alway Murdock. When Face stayed out too late fraternizing with the nurses, it was Murdock who would cover for him with Hannibal, even though Hannibal knew the truth. When Murdock disappeared one night, it was Face who found him just sitting in his chopper, staring blankly into the back, obviously too upset to talk about what happened that day. Face did nothing but just sit with him for the rest of the night, but he knew it was needed.
The first time it happened, it was pitch black when Murdock lowered the chopper smack dab in the middle of a hot lz, just skimming the ground enough for the three of them to pile in before rapidly rising high again out of range. "Thanks for saving my ass, Murdock!" Face yelled as they rose above the trees, all three of them firing out the sides of the Huey. And when Murdock howled and retorted, "No problem, brother!", it caught Face off guard. Hannibal and BA both pretended not to notice to look on their Lieutenant's face.
Forged in the fires of hell and war, the bond of brothers. Now and forever.