I frequently hear people ask if someone can be forgiven for their cheating. Can they be trusted again? I sadly, don't have a solid answer on that. But I have a few opinions on the matter.
Can you forgive them? That's up to you. I'm sure they're worthy of forgiveness. Hell, sometimes holding a grudge against someone harms you more than it harms the person for whom you are holding the grudge. I tend to be one that doesn't hold grudges. That's not to say that I completely forget about the transgression. If you've done me wrong, I may not still be pissed about it, but I'm not forgetting about it, entirely, either. It's a strike against you. So, if you're in a relationship with someone, and you've been together for a considerable amount of time and your partner cheats on you, you'll need to figure out whether that's a forgivable offense or not. Is it their first time doing this? Their 20th? Did they tell you tons of lies or bring home any diseases? Was it a "Wham-bam - Thank you ma'am!" thing, or an ongoing affair? There are too many variables.
The bigger question, though, is whether this person can be trusted again, or not. Again, that may depend on the individual, but I think it all boils down to trust. If your partner has lost your trust completely, then it doesn't matter if they will or will not cheat again. You aren't going to trust them. Unless that trust can be restored, that's going to be a huge obstacle to a healthy relationship. So, is there something that your partner can do to regain your trust? Maybe. Setting up some sort of accountability arrangement, where your partner checks in with you frequently might help, but it might also cause them to resent you, even if they brought this on, themselves.
I, personally, am not inclined to believe that a cheater will just cheat once. I've seen too many cases of people who were repeat offenders. I haven't heard of too many instances where it was a one-time thing. I think one thing which many people overlook when they are dating their partner is whether or not their partner cheated on their previous partner.
I've seen a few cases where a man or a woman was cheating on their partner with someone else and then ended up dating or marrying the new person, with whom they were having their affair. Basically, that second relationship was a direct product of infidelity in the prior relationship. Then they seem surprised when that man or woman cheats again. What were you expecting? Why did you think it would be any different when they were dating you?
Some people just don't seem meant to be in a monogamous relationship, but they put forth a modicum of effort to at least appear like that's what they're looking for when, instead, they should just stick to casual relationships or open ones. I don't know if this is because there's this perception that society demands that people be paired up and with the goal of being married, or what. I've seen a few people, though, who I just felt like they really should just stay single.
That quest for variety for some people - that need - is just too strong. It's not always that they don't love you or love you any less, or that the sex with you is inadequate. They just see that new person, and they must be with them.
In some cases, the cheating is kind of your own fault. I say "kind of" because I think that the cheater is always responsible for their own actions. But sometimes the person being cheated on plays a role in their motivation to do so. If you're refusing sex, or you're distant, or never available, your partner is going to be left wanting. They may be patient and stick it out, or they may just say "fuck it" and find their fun somewhere else. I think communication can do a lot to help prevent that. If you're refusing sex, or you're distant, talking about why that is, may help. Rearranging schedules as much as possible so that you're together more can help too. But, realistically, some things just can't be resolved. Maybe you're stuck with the shift you have. Or maybe you have a medical condition which makes sex impossible. Well, in those cases, you're going to have to do some creative problem solving.
What if you can't perform sexually? First of all, go to a doctor and make sure there's nothing seriously wrong. Also see if there's anything that can be done, and, if so, do it. If nothing can be done, then I'd suggest finding ways to please your partner, sexually, which are still possible for you. If you can't have actual penis-in-vagina sex, then stick to oral and manual stimulation. Find some way to make it work. If you are unwilling to, or just can't, maybe discuss opening up the relationship. I think it's unreasonable to expect your partner to live a celibate life. And I say this with all due respect to those who are unable to have sex. It's terrible that you're in that situation, but don't drag others down with you. I know that sounds heartless. It's just the way it is, though.
If you have scheduling conflicts, you owe it to your partner to be available to them somehow. Personally, I think your partner should come before your job, or your hobbies, or the rest of your extended family. You've chosen this person to be a part of your life, so be a part of theirs. Find a way.
None of this, though, gives an excuse to cheat. At most, it explains why people cheat. Sometimes people cheat because they never discussed their concerns with their partner. Had they discussed them, the problems might have been resolved, and they would have lost the desire to find outside physical release. Sometimes it's not that simple.
Once in a while a couple gets paired up and they have sex, then one of them realizes that they have some kinks. They have a fear of sharing these kinks with their partner, whether they're afraid they'll scare them off, or the kink is just too taboo and embarrassing. But, still, this is a communication problem. Discuss your kinks with your partner. They may be willing to indulge you. They may be curious about it. They may be totally against it. You won't know until you ask. If they aren't too open to the idea, are you really any worse off than you were before you told them, though? With most kinks, it's not imperative that you engage in them. With others, it's basically a requirement. Though, if that were the case, you wouldn't have gotten this far, and been in a relationship for any length of time, without having introduced the kink. So, I think you can manage without it. If you find that it's really important, though, talk with your partner and if they aren't open to it, discuss finding a way to satisfy your kink outside of the relationship.
Since the motivations for cheating don't tend to disappear on their own, I think there's a strong chance that a cheater will always be a cheater. Unless they improve their communication skills or get over their need for variety, or suddenly learn to respect their partner enough to remain faithful and monogamous, I can't image they'll suddenly break their bad habit. Once they've gotten over the guilt of that first time that they cheated, all future times get easier and easier. Basically, I guess, the answer seems to be, yes, a cheater is always a cheater.