If the relationship isn't abusive and both persons get along with each other, values each other, are seriously committed to each other, have matching personalities, love each other unconditionally no matter what and understand each other's trouble, difficulty, and don't judge one another, then there is supposed to be no doubt that they are best friends. Let's suppose that in a straight couple that goes by this ideal, one of them says to the other "I present you my best friend." The other couple with no doubt will feel betrayed. I know there are some controversies with that some people say that in a straight couple, one of them could have a "bestest best friend who is the same gender that doesn't include his/her partner." Maybe the behavior of best friendship between two people that are the same gender is what led to homosexuality. How can you have a friend who is a better friend than your own partner if you are under the ideal of this question posted on top? It doesn't make sense. That could be one of the top reasons why there is so much divorce and break ups, probably because people will choose a partner who only looks beautiful and not care about anything else. Choosing a partner based on the look is not unconditional love. Love should be felt with the heart, not with the eyes.