Hi Marie27,

You are probably aware that there are many more sad love-songs in traditional music than there are happy ones. ("Sorry the Day I was Married", comes to mind!) "Eileen A-Roon" is pretty, but most appropriate if you're of Irish descent. And it doesn't have a refrain that repeats. "Roseville Fair" would be more appropriate for the reception. ("Here's a glass to all true lovers...")

In reading over your post again, I see that you probably meant "beside" an oak tree, not that the oak tree would be singing! (interesting image!)
Best Wishes to You Both!