My boyfriend or girlfriend cheated on me, should we break up?

YES. Although I do not agree with the term "once a cheater always a cheater", I do believe the bond of trust has been broken once cheating has been involved, and I think leaving is hard but necessary

Yes, once a cheater will always be a cheater. If he respected you he wouldn't do this to hurt you. I would move on. It will be hard on the relationship if you knew they have cheated.

If you let them cheat once, they'll do it again. I know this as personal experience. I would leave him because they know they can take advantage of you.

A partner cheating degrades the trust you have with them. Take the time you need to come to accept it and figure out your emotions, express how you are feeling. If you feel that you may never be able to regain that trust again, ending the relationship may be the best course. If you feel you could rebuild that trust, perhaps work on the relationship. Whatever you do, do it at your pace.

Well first you should talk it out. Then see where the two of you all stand. How much do you really love eachother and then go from there

Honestly, yes because cheating breaks trust and you can't have a relationship without trust. It's just not healthy.

Can you answer the following; a) Have you ever cheated on your partner, even emotionally? b) Is this the first time they have cheated on you or in another relationship? c) Was it it a once-off thing or has it been going on for a long time or where there multiple partners? d) Were they sober when they did it? e) Did they cheat on you physically or emotionally? f) Did they cheat with a previous partner? g) If yes for the above asked question, are they over that person? Based on your answers to these questions, do you feel that you and your partner can work together to mend the relationship?

Take a time-out. Calm down, and than talk, calmly. Hear what your partner has to say. Don't start jellying, simply let your partner do the talking.

Yes. I am a strong believer of loyalty in relationships. People will say depands on your situation. But always remember if your partner has done it that means they have it in them what makes you think they will not do it over and over again.

I think you should, since that bond of trust obviously isn't there anymore. You need that bond in a relationship, and you're obviously on thin ice.