Bailey's fiancé, Toby, is the moon to Joe's sun, the person who comes the closest (Lennie thinks) to understanding her grief. He's also someone Lennie is attracted to, which complicates things tremendously. Lennie would probably have been able to resist him once she started up with Joe, except that Toby keeps confronting her, ostensibly to apologize, and then says things like "It's just that I can't stop thinking about you" (21.24). Sigh.
Toby pulls off the feat of remaining a sympathetic character, despite the fact that Joe is the love interest we root for. Toby's quiet, he's good with animals, plus he never takes advantage of Lennie—she feels as drawn to him as he does to her. And we know he's in so much pain. So yeah, dude's hard to hate.
Even if you're not on the Toby bandwagon, though, this character makes himself un-hateable by trying to make things better between Lennie and Joe. Check it out:
He looks over at me for a moment before returning his eyes to the road. "I watched you guys that night in the rain… I saw it, how you feel." (28.70)
Toby, who feels physically pulled toward Lennie, tries to help her be with someone else because he recognizes that she and Joe are in love. So he's definitely a good guy. He tells Lennie this in true Toby fashion—by looking away, and with as few words as possible. It's a gesture that's all the more heartbreaking because the reason he can recognize the love between Lennie and Joe is because it's what he felt for Bailey.
It's going to be a long road to recovery for Toby—losing your fiancé and unborn child is not an easy thing to recover from—but while he stumbles around in the beginning of the book, projecting his grief and feelings for Bailey onto Lennie, by the end, he takes on a less passionate, caregiving role for Lennie, treating her like his little sister. And when he does, we can tell he's finally headed in the direction of recovery.