There are a lot of variables to consider.
Age and life circumstances can play a major role.
For example two high school sweethearts go away to different colleges. They plan to continue to maintain their relationship long distance. Eventually one of them begins to socialize and makes friends on campus, attend parties, and at some point meets someone they're attracted to. LDRs require maturity and self-discipline.
In hindsight it's obvious the odds were against maintaining a long distance relationship for 4-6 years especially at ages 18 or 19. It was an "unrealistic expectation". More often than not one person cheats in this situation or they break off their current relationship because there is someone they want to pursue a relationship with who is with them
If that relationship fails months later it would make no sense to get back with them because the issue/distance that led to them cheating remains.
Other key factors such as: Do you believe (you) contributed in some way to their decision to cheat. In other words had you "stopped" being the person they fell in love with? Were you neglectful, took them for granted, mistreated them in some way, no longer were affectionate or romantic? How did you learn about the cheating. Did they approach you one day out of the blue and confess? or Was it because you "caught" them?
If you caught them it begs the question of: What would have happened if you had not caught them? In other words the cheating would have continued.
Is your mate showing (genuine) contrition, demonstrating a wiliness to be transparent by bending over backwards to assure you, understanding that it will take you time to trust them again, and most importantly they can fully explain what caused them to cheat and why they (know) given the same set of circumstances they would never do that again.
It's probably best to take a couple of weeks apart to figure out whether or not you can forgive. Too often people offer "instant forgiveness" only to learn down the road that they can't forgive.
They were shocked at the betrayal and the thought of a breakup or divorce was too much to bear at the time.
However I believe for me personally I would not give a second chance and the reason why is because I believe if you're in an "exclusive relationship" you give it your all and if someone cheats on you after you've given your "best" and that wasn't "good enough" it's unlikely I could trust them.
There are basic three things that keep people from cheating:
1. Being "in love"
2. Not wanting to risk losing that "special someone".
3. Imagining how hurt they'd feel if their mate cheated on them.
"Never love anyone who treats you like you're ordinary."
- Oscar Wilde
Clearly if someone cheats on you they don't think you're all that "special".