I need help finding a song please?!?

My boyfriend sang a couple of lines from this song he suddenly remembered, but we can't find it anywhere online and it's doing our heads in! :P I didn't recognise it at all, but apparently it goes "why do I love you, I just don't know" and pretty high pitched it seems? With a pause between "why do I love you" and "I just don't know" as well? He might have got the lyrics wrong though, I'm not sure! He says he thinks it's a rather obscure song. Anyone got any ideas? Would be very helpful! :) Thank you!