Seeing as Mark Gruenwald felt that Captain America didn't need a civilian life (he promptly ended Cap's relationship with Bernie Rosenthal), it seemed the only real romantic prospects left for Cap during this era were in the adventurer community. Hence Cap's improbable relationship with Diamondback, one of the villainous Serpent Squad.
Mark Gruenwald had an obvious interest in workplace dynamics, and one of the first things he did was introduce a new Serpent Squad, featuring villains who were just out to make a buck and get health insurance, via gigs for hire. It didn't really catch fire, but Gruenwald followed up on it by showing more of the logistics behind Cap's leadership of the Avengers, and the Red Skull's ongoing relationships with his newly enlarged group of cronies. Only the Red Skull's crew reached the level of passably interesting so far.
Ignoring the fact that simply being a member of the Serpent Society arguably makes Diamondback an accessory to murder, Gruenwald seemed to have positioned Diamondback as a possibly love interest from the start, introducing her as a relatively benign mercenary who began crushing on Cap almost from the start. It's a little hard to buy that a goody-goody like Gruenwald's Cap would ever show much interest in such a character, but readers were, I think, willing to suspend disbelief so that we could see Cap doing something in his off-hours besides attended meetings with architects regarding the new Avengers headquarters.
The big problem is that Diamondback is a pretty one-dimensional character, even by Gruenwald standards. (Character creation definitely wasn't Gruenwald's forté.) I really don't have a thing to say about her.
For all that, I'm generally enjoying reading Gruenwald's run at this point. He didn't push the medium forward any, but Gruenwald's lack of pretensions and love of classic superhero serial storytelling make his run a pretty easy read.