I found the one I was looking for. It may be what you want, but it's not acapella. The song is called 'The Way Love Is' and it is written by Hugh Moffatt. The first couple of verses go:

I've been down and I've been lonesome
I've been around and I've been home some
When I say that I love you
I know what love is

I love you and my love is true
And I know that you love me too
I don't worry 'bout tomorrow
I know what love is

I have it on a few Moffatt albums - 'The Way Love Is' Columbia, 'Live and Alone' Brambus and 'The Wognum Sessions' Strictly Country. The last may be what you heard - he is singing with Michel Jansen and Brent Boyer, but it is not acapella. Others may have covered the song.

I hope it's what you want, but I can now get on with other things without it going around in my head.

Cheers, Stewie.