I think it's wistful thinking to believe that you can make a woman be more faithful to you just from good d1ck. Sure, it'll help. Sure, they'll probably come back for more at some point. And they'll tell you whatever they sense will work best to boost your ego enough that you'll give them validation in return.
Your best bet to keep a girl faithful is to bail out as soon as the honeymoon's over (almost every girl is faithful when they're 'in love;' you might can stretch that out to 18 months if you know what you're doing). Beyond that, you have to be a really solid dude all the way around (especially if you haven't knocked her up in that time period)--and more importantly you have to have selected the right girl at the right time in her life and be at a point in your life where you're not gonna hit a down stretch that'll set off her hypergamous alarms.
