This post is Peppered with spoilers for Borderlands 2. It's an awesome game, and you should play it.
When you create a character, in games or in fiction, you have to give that character to your audience. They interpret them in ways that authors often can't expect. In games, when you give players a character, they often have exaggerated qualities, both good and bad; this is especially true in power fantasies. If you take that character, and insert it into a sequel without giving the player agency over them, a new issue arises. It's the difference between a reflection and a photo. As an author, you may have to further exaggerate those qualities. This worked in Metal Gear Solid 2. It has mixed success in Borderlands 2.
Borderlands left the original Vault Hunters blank slate; to be interpreted by their mechanics and their aesthetics. They didn't have a ton of dialogue, and couldn't truly respond to anyone. In the followup, We have a new set of Vault Hunters to play as, with the veterans participating as mentors, quest givers and leaders of a resistance. Each one has their identity initially obscured and then revealed in a way that allows the player to realize how much they missed them.
Each other them have been given new characteristics. Lilith, whose image and identity revolved around the word "Seduction," now feels like a new member of the X-Men, exploring new powers with excitement with very little care about the new risks and responsibilities they might require. Roland has settled into his role as the Leader of the Crimson Raiders nicely. He seems to have taken to heart the role that Atlas played in the last game and wants to protect those his ex-comrades have misplaced and abused. Mordecai has settled into solidarity with his friend Bloodwing, relishing in alcohol and ammunition. Brick has become a bandit leader, trying to focus chaos into order, while at the same time trying to rationalize the insanity Pandora seems to draw so easily.
Three of these felt like major improvements, but Mordecai felt like an afterthought.
Every time you meet a new character, with the exception of Clap Trap, they have an introduction banner giving silly editorial comments about them. "Marcus; No Refunds," "Tannis; Insane(ly smart)," "Zed; Do no harm."
The old Guard have these, too. "Lilith; AKA the Firehawke," "Roland; as Commander of the Crimson Raiders.." But Mordecai's is a little more focused. "Mordecai, and his BFF bloodwing."
And I loved that. In Borderlands 1, Bloodwing had a mechanical relationship with Roland, but you never heard him treat her like a pet. It felt like an asymmetric partnership (still an action skill that I loved). But in BL2, you never see him send her out for a kill, and then 3 chapters later, you have to go rescue her, and instead of partnering up, Mordecai stays in a perch and snipes from a distance. This does not emotionally or mechanically compute.
When we head into the wildlife preserve, he gives a decent excuse; that he knows Bloodwing well, and that she can handle herself. But in the end, and this may have been the intention; Mordecai is deceiving himself, and the fact that he's not there when Bloodwing dies has me unconvinced that he loved her. He's living in a fantasy that he and she can handle the problem, and instead of taking action to help, he leaves it to a (competent) stranger to rescue her.
Truth be told, I can't tell if this is brilliant psychology that highlights the deep insanity of Pandora, or if it's a flaw on the part of the writers, but it's hard for me to love Mordecai as much as I did when I first played as him in Borderlands 1.