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Benedick Mountanto is a bit of a jerk. He's also kind of awesome. He's also a bit of a jerk. He's also... ugh, we're starting to feel like Beatrice. And Benedick mirrors Beatrice's ambivalence right back.
When we first meet Benedick, he’s not particularly notable for anything other than his sharp wit, which he uses to happily and insensitively indulge his mean streak. He loves to play the role of the director—he even tells Don Pedro about the lines he should speak when Don Pedro is courting Hero on Claudio’s behalf. Most things are a joke to him, and he cares very little for others’ feelings (remember how he teases Claudio instead of comforting him when he thinks Don Pedro has stolen Hero?).
He especially likes to be mean when it comes to matters of love, probably because he spends most of the play railing against marriage:
BENEDICK Is 't come to this? In faith, hath not the world one man but he will wear his cap with suspicion? Shall I never see a bachelor of threescore again? Go to, i' faith, an thou wilt needs thrust thy neck into a yoke, wear the print of it, and sigh away Sundays. (1.1.193-198)
His reasons are complex though; while Beatrice thinks no man will ever be good enough for her, Benedick seems to be more hung up on not being tied down.
Things change for Benedick once he hears Beatrice might love him. He decides to go after Beatrice not because he’s in love with her; instead, he’s focused on proving that he’s not scornful and proud. Once he comes around to loving Beatrice, his clever, sharp nature dulls a little bit (as in the toothache scene). Beatrice is afraid to be vulnerable, but Benedick approaches lovesickness in a much more conventional way.
But as he tries to write Beatrice poetry, he realizes he’s just not a conventional lover. It seems the strangeness of the formalities of romance is what makes love alien to him—not any particular fear of love itself. This is perhaps why he’s willing to be so forward in the love affair. For example, when Beatrice calls him in to dinner, he’s sweet, and he’s also the first one of the pair to even confess that he’s actually in love.
The real turning point in the play for Benedick is at Hero’s (first) wedding, when he chooses to stay with Hero and look after her, instead of automatically leaving with Don Pedro, Don John, and Claudio. At that moment, he makes clear that his allegiance is actually now also to the woman he loves. He even agrees to challenge Claudio.
Beatrice is willing to give up love over Hero’s reputation, and Benedick is willing to give up his friendship with Claudio over Beatrice’s love. Once he’s been moved by love, his loyalties are clear to him and he doesn’t exhibit any of the misgivings that make Beatrice’s love so tentative. This is shored up in the final scene, when he’s the one that puts their love to the public test. While Beatrice is ready to deny their love, Benedick asks again if she loves him, and he seems relieved when the letters show up.
He even declares the sudden saving of their love affair to be "a miracle!" He's coordinated a marriage ceremony with the Friar, and happily tells Beatrice that he’ll wed her, though he still teases her that it’s only out of pity. Thus Benedick is a lovable character who keeps his wits about him, but he lacks the depth and conflict in his love that define Beatrice’s approach to romance.