Escalated into friendship
You see, those two phenomena of human soul are rather peculiar and people rare feel the difference between those. They are rather alike and so it is sometimes hard to realize where the friendship and where the love is when it is about heterosexual friendship. That is why it is common for such friends to fall in love with each other and in counter.
It is common for people who were friends to realize that they feel something more than friendship and it is also common for them to realize that they confused love and friendship. People meet each other, they get to know each other better and they are a couple but they suddenly realize that there is no love between them, there is something else.
It is rare when people are able to be friends after they have broke up, it is hard to be a friend for the one you are in love with and with the one who feel nothing like love about you. It hurts and a few people are able to do it. Though, there are those who broke up because both of them realize that there is no love and they remain good friends.
It is great when one can be a friend for another no matter the fact they used to be lovers. It is great though it is wrong to confuse love and friendship. So, love escalated to friendship is another phenomenon conditioned by likeness between friendship and love. Friendship is a love without wings and sometimes people fix wings on friendship and confuse it with love.