Friends who are enabling you to have a 3rd party relationship when you are happily married are not real friends.
First, a real friend will value the essence of family and will not support you in destroying yours by any means possible. They will remind you of why you should not do it even if there is temptation around.
Second, those who are enabling you to have a 3rd party relationship are probably miserable in their own love lives. Maybe their marriages suck and they don't know how to fix it. Misery loves company so if their marriage is broken, they would like yours to be broken too so they won't feel as bad about theirs.
Third, perhaps they really lack the discipline, devotion, and commitment to be a faithful and loyal spouse so they wanna corrupt your moral values too. Again, misery loves company.
Remember, when your family gets broken, those "corrupt friends" will not be there to support you anyway. They will just tell you that it is fine to cheat on your spouse that you did the right thing, even if you are already accumulating lots of karmic debt.
Choose your friends wisely.
This is not about being hypocritical or morally superior. It is about being friends only with the people who wish the best for your life, even if that means being "killjoy" about certain situations.
Founder of Astral Crystals.