Cheating is not so black and white. There is a phrase lots of kids on here like to throw around, you've probably heard it. "Once a cheater, always a cheater." The problem with this phrase, is that it's just not true.
There are various kinds of cheaters. Not all cheaters are the same. There are people who honestly just make a mistake. This doesn't mean the cheating is justifiable, but we are all human, we all make mistakes. Even the best of us make mistakes.
And some girls will even come on here, like the one above, who says, "If he cheats, it means he doesn't love me." This is not even remotely true. If you do any research into the male brain, you'll fine that males do not equate sex, with love like women do. Men are perfectly capable with carrying on with affairs, having sex, and having zero emotion doing so. They will be in love with their partner, but mess up, have sex with someone else... and that's all it is. Sex.
Then there are habitual cheaters. People who just don't care that they cheat, they cheat on every boyfriend/girlfriend they've ever had, they don't feel guilt or remorse. <--- Those are the cheaters to which the above phrase talk about.
I'll admit it. I've been a cheater. I've betrayed a past partner. I learned from it. The guilt, the pain, the misery I had to go through, deal with, and then the guilt I had on my own shoulders for years after the fact... I've never cheated again. So, once a cheater, not always a cheater.
As a person, it's fairly easy to see what category of cheater your significant other falls into. If your significant other expresses extreme remorse, and repentance, and PROVES and shows to their bf/gf that they were wrong, and know it, and will never do it again, yes. That person deserves a second chance. I also think that people who confess on their own, and who are not found out, deserve a second chance.
If your significant other expresses no apologies, doesn't seem to care, doesn't acknowledge it, lies about it, and generally gives off an "i don't care" attitude. Then no. That person does not deserve a second chance.
And in regards to the people who DO get second chances, that's the only chance they get. Do it again, and you're done for good. There are no more chances after the second.