Even though people have different opinions on this topic, I think infidelity is wrong in all situations. There are several reasons why a person may cheat on their partner: Distrust, heartbreak, lack of communication, and so go on. It's quite challenging to determine whether a person is naturally disloyal, but I don't think a person is inherently unfaithful. People usually cheat on their partner to add more excitement to their lives or because they are stuck in a routine and need to try something new. But infidelity sometimes doesn't involve only a sexual relationship, but a romantic one or it doesn't has to be necessary sexual. This is important because we tend to relate infidelity with a physical connection when sometimes is worse the complicity or bond it can arise. For me, cheating is selfish and dishonest, and I don't think there's any justification for cheating on someone. Infidelity can break relationships and families and lead to emotional distress, anxiety, depression or increased risk-taking behaviour.

Note that infidelity and sexual promiscuity are NOT the same thing. Infidelity is simply not respecting the rules and wishes you and your partner(s) laid out prior. This is almost always an agreement to be sexually exclusive with one partner. And generally includes things about other forms of romantic or sexual interactions. But it could also mean being sexually exclusive to multiple partners. Or some 1-to-1 exchange to keep sexuality balanced. Or an agreement that your partner must meet additional partners first. Or that additional partners must join in. Regardless of whichever rules you agreed on, infidelity is betraying this. Sexuality is a very highly emotional, highly charged part of human life, so sexual infidelity creates a ton of drama and leaves a ton of scars. Honesty and fidelity are the best policy. If you don't like how the rules are set up, communicate with your partner about changes.