two people have been breaked up ,but,just like know themselves,so they feel unhappy

Because it would hurt the friendship

If friends can be lovers, the those people who are are lovers who are also friends. Therefore, the logic defeats the first part of your statement. Also, you can say the person you love is also your best friend, so I don't know what you're on about.

because lovers to friends it's a way back!!!

Just get over it and find the next one, bro.