Bob has visited a brothel every night since it was legal for him to. Alice has never even touched a male with her bare hands. They will become the Official Couple.
Downplayed: Bob is the most sexually active character in the series (compared to the others, who aren't promiscuous themselves), but ends with Alice, who only has sex with someone she truly knows and loves.
Bob knows he'll eventually settle down and stop his reckless lifestyle, and wants to be with the girl that'll definitely be faithful to him.
Alternatively, All Women Are Lustful in this setting, therefore one that isn't constantly looking for sex is seen as a prize.
Bob thinks that promiscuous women have loose/big naughty-bits.
Zig Zagged: Bob only says he's been with other ladies to his guy friends, but we've never seen him...oh, never mind; he IS sexually active! But, look; so is Alice! Guess she's no longer the love interest...unless it was Not What It Looks Like and she is still dedicated to Bob.
Bob and Alice are both virgins, or they've both had sex with other people.
Neither Alice's nor Bob's sexual histories are commented on in-story, as they are not relevant to the plot.
Being a slut or a virgin is neither seen as good or bad.
Enforced: "The guys will sympathise with Bob for being able to pick girls up so easily, and the girls will see Alice as a kind-hearted role model that'll win in the end. What could go wrong?"
Lampshaded: "Bob, if it wasn't for this little thing called the 'Double Standard', Alice would've mounted your head on a pike by now."
Invoked: Bob isn't officially dating Alice, and his best friend is having his bachelor party at the local strip joint...Alice will understand if his hormones kick in, right?
Defied: "If Bob thinks it's okay for him to fuck all these other chicks, why shouldn't I be able to pick up a few studs myself?"
Discussed: "If Bob knows that Alice will always be there for him, why is he always with other chicks he knows he'll only have sex with?"
Conversed: "Bob's such a hypocrite! Why can't he be as faithful to her as she is to him?"
Deconstructed: Because of the Double Standard, Bob suffers from a bad case of Madonna-Whore Complex and always thinks of other women when he makes love to Alice because he can't have sex with a woman he respects. He ends up cheating on Alice constantly and their relationship goes sour, especially after their kids find out his lifetyle. Both end up bitter and miserable.
Reconstructed: Acknowledging that such a relationship is hurtful to both and pretty much going nowhere, both part ways amicably before having kids and go searching for a more fulfilling relationship that both would enjoy.
Plotted A Good Waste: Bob's activeness is due to a Freudian Excuse. He never felt loved as a child, and seeks to fill the void with physical pleasures. Alice's dedication to him causes a revelation that develops his character and become a wonderful couple.
Played For Laughs: Bob plans to have a romantic evening alone with Alice...until one of his old 'conquests' shows up at his door, wanting to start an actual relationship. Cue Bob arguing with himself and a possible Cat Fight between the two girls.
Played For Drama:
Bob's virility leads him to catching an STD, which he passes on to Alice. Even though Bob has had a lot of sex in the past, Alice has had only a little with him, and will never be able to enjoy it again.
Alternatively, one of Bob's girlfriends is pregnant with his child, and doesn't want an abortion. Will Bob choose to be with the mother of his child, or the still-faithful Alice?