A song in the movie and when the movie was made

I was wondering what the tune is called that is played in some parts of the movie, like the part where Roger envisions Diane when he's about to say he can't marry Clarice because he's not in love with her. That song is very catchy. I found myself singing it this morning and adding my own parts, because I didn't know how exactly it went. Haha I was also wondering if this movie was made while Mary-Kate and Ashley were still starring as Michelle in Full House, or after the show went off the air?