Why is there always a "third party?"

Since we deal with different people in our lives every second of the day, expect that there's always a third party in any relationships, may it be your relationship with your friends and loved ones. So come to think of it. Our partners are human beings. Since we have learned to love them for who and what they are, that simply means that in one way or another, they have qualities in them that make them lovable. Hence, in a relationship, expect that there's always a third party where your partner can meet other woman and same as you, you can meet other man. Tendency is these "other people" or "thrid party" would most likely fall for you and there are those who would fall for your man. Now, since this is one reason why third party is inescapable, then everything must come between the lovers themselves. Lovers should avoid these temptations to make their relationships worthwhile. Unfortunately, we belong to an imperfect world. So what we just have to do to avoid our men cheat on us? Just love them and make them happy at all times. And how men can love their woman? Same thing! love conquers all. :)