Why do you want to cheat? I think understanding the logic behind it might help you understand a solution.

Reddit really vilifies cheating as pretty much the absolute worst thing you can do to another human being... But I honestly believe that people who cheat don't do it because they purposely want to hurt the other person. I also think it's possible to want to cheat and be in a happy relationship and/or to be very much in love with your partner. I'm sure many people will disagree with me here, and would rather believe that people who cheat are heartless, brainless jerks who should be thrown on the street and shot. But I'm of a different mindset and would rather approach this with empathy and try to understand where the mindset comes from.

I just think everyone provides certain things and the things you get out of a relationship are not always the things you need or want. I think it would be unfair to expect one person to be your everything in a relationship. So when confronted with the possibility of cheating, I would ask myself what this new person could possibly provide me with that my current partner doesn't (usually excitement, entertainment, a "spark"/physical/emotional connection, or potentially different/exciting sex). Then I logically think my way through this - what are all the things a new person couldn't provide me with that my partner does? (usually love, care, empathy, compassion, loyalty, friendship, etc etc). The obvious choice then becomes to pick my partner because a new relationship often provides things that are temporary or fleeting, whereas my partner has provided me with long-term benefits.

I think about the gaps in my current relationship and see if I can fix them (am I unhappy with what I'm getting or do I just want more? Am I being greedy?) or come up with solutions to work towards getting what I want (I miss the spark so I'll plan more dates and remind myself every morning why I choose the person I'm with), or I (personally) fill gaps everywhere I can with my friends (I miss being able to tease or joke with someone, so I'll tease/joke with my friends, for example). This one's tricky because sometimes I get myself into "emotional cheating" territory, where I need to take a GIANT step back from a friend when I realize I've been relying on them too much to support me in ways I should be able to support myself (or hopefully, even better, you have a partner who supports you and who you feel like you can talk about anything with) - like when I went through a major depressive episode and realized I needed to be stronger and that my unhappiness could be fixed by working on fixing myself more. I think about how cheating would make my partner feel, and the consequences of him leaving me and how absolutely heartbroken I would be knowing it's all my fault and that I've hurt him.

At one point, I really liked a woman who I met at a party and had recently (a half year prior) discovered how much I identify with polyamory. I asked if my partner would consider polyamory and he said absolutely not. This might be an option for some people though, and would recommend anyone considering it to check our resources like /r/polyamory, and to be honest with themselves on if they could make this work, rather than jumping into it. Polyamory and monogamy both have their pros and cons but I would not use polyamory to magically try to fix a relationship that is broken.

At one point, I realized I was very unhappy, and tried ending things, but he refused and told me he would never leave me. So I did the right thing and worked on remaining monogamous with him. I don't put myself in positions where I'm tempted to cheat: I rarely go out, I never spend time with people I'm attracted to one on one, and every time I get negative thoughts, I do something nice for my partner instead, which might sound messed up, but it's a way for me to redirect my feelings. Like, I'm feeling very sexually frustrated, so I'll make him a nice dinner. He's always appreciative, so I'm reminded of a quality I love about him, and maybe if he's more relaxed and has less on his plate, I might get lucky too, so it works in my favour.

I think people on reddit must have a huge amount of self-control, since they can say "I just don't do it" and that works for them. Or are maybe they're in and out of many short term relationships? I've lived with my partner for a decade and have had the opportunity to cheat at least a dozen times. I realize this will continue to come up over and over again. Oddly, the thought that this is a reoccurring thing also makes it easier to turn down.... Because I know I need to get good at saying no and doing what is best for my relationship. I also remind myself that relationships do ebb and flow, and that the feelings of NRE are super powerful but fleeting. It's usually the NRE high I miss more than anything, and reminding myself it's temporary gives me one more reason to say no, because I would just be in the exact same point I'm currently in, but likely, with someone who is worse suited to me.