Most Helpful Girl
If its an open relationship, you still have a conversation with your partner about boundries, if one those boundries are disregarded, its cheating.
For example, an open relationship may include sex outside the relationship and sex only. But then one partner finds out the other has developed a close emotional and sexual relationship with someone else.
Most Helpful Guy
Yes it totally is. I have a friend who was in an open relationship with someone, and even tho she was sleeping around her boyfriend convinced her she was the only one she needed and that she was the only one that he wanted. Well it later came out that he had been for some reason hiding the fact that he was fucking someone else too. She broke up with him quickly after.