Falling in love isn't unhealthy at all. It is wonderful. But if a person is unhappy in their relationship to the point that they feel the need to seek out other people then they need to leave it. Your feelings are not unhealthy but your actions are selfish. You two need to realize that you are hurting people by what you are doing. He needs either tend to the relationship he is in and set boundaries with you or end the relationship he is in and see where things go with you. I think your attitude would change if you were this other gal.