In my life, boyfriends and crushes have come and gone. My best friend from middle school, my girlfriends from college, and the like-minded women I met early in my career are still my best friends and confidants. I really do love them like sisters. Last year, one of my friends' husband sent me flowers, a hotel key, and a note asking me to meet him one afternoon. I gave her the key and the note... and she lived with us for a month while she was letting it all sink in and making arrangements to start a new life without him. I put her first.
Ask yourself these two questions. Do you want your friend to be with a guy who would disrespect her this way? Do YOU want a guy who's already shown you that he'll hop from one girl to another? My guess is that if you love your friend and yourself, your answer to both questions will be no.