I married my best friend in a similar situation.
She was dating a friend of mine. We hung out alot. Her and I became closer than he and I. She and I both started having feelings for each other as she and the current boyfriend grew apart. One night we kissed. Was amazing but she was scared to part ways with him. It was hell for me for a few weeks but finally I forced her to decide. She picked me and the rest is history.
Rock Chalk Championship.