So, I believe in every relationship, unless you live in a village or at a farm, your girl will see (and meet) guys she would fuck and date under the right circumstances. She being loyal to you and not fucking others is something you must maintain...using the things that Chase write in his article : "How to Prevent Cheating"..and hope for the best.
Also I'd like to add, fuck her like an animal and fuck her like a pornstar. She MUST NOT see other men and thinking to herself "My boyfriend provides a lot but this sexy motherfucker seems like to know how to fuck me on all 4s anally, cum in my ass and then put it in my mouth". YOU must be the one you does this (If you want to have beside you a woman who's so high quality that dudes as sexy and manly as guys like Javier Bardem or Oliver Martinez would wanna fuck).
I'm pretty sure Hector and Chase mention the thing about awesome fucking on your behalf.
As for If you can forgive it...well, I will put it vividly in your mind to decide yourself.
Hopefully, at least once in your lifetime you've been in love with a girl.
Imagine being great with that girlfriend and suddenly you learn a guy fucked her.
Imagine...your precious girl you've been in love...that some days ago, when she told she just went for a drink with her coworkers, Mark was with (Let's call him Mark). You know Mark, you can picture his face, hear his voice.He's an arrogant motherfucker, trying to climb his way through the corporate ladder and throwing people under the bus on his way. Or is an arrogant motherfucker, artist with charisma and devil may care attitude. You could see in his face that he wanted to bang your girl, given the opportunity.
And then, you learn that your babe, flirted with Mark, was isolated by Mark, and then got on her knees and took his dick on her mouth. Maybe it was worse than yours, but still it's a dick. Not something you particularly like in your girls mouth (unless it's yours..!). After giving him a blowjob the same way she does for you, Mark bended her over and started fucking her from behind. Her back was arced, he was pulling her hair and she was moaning. After pounding and spanking her ass, he told her he wanted to cum got out and covered your girls face with cum.
And the next day she kissed you on the mouth. You tasted Mark's cum. You've been cuckolded. Some motherfucker dominated and ejaculated on your girl. She just became something of the past.
I've learned, sadly the hard way, these kind of thoughts, a guy you may know or not fucking your girl, it's not something you want to live with. They rot your soul slowly.