As the only member of the family who will not hate me after I do what I have to do, I would like to invite you to a little wedding. Mother and Father are trying to marry me off to some German idiot that Cissa dumped so she could have Malfoy, only I don't want to marry him either, so Ted and I came up with a plan. He's going to marry me first, so that the German can't have me.
I'm leaving the family behind, like you did, so that I can marry Ted and have a happy life full of love and everything else. So if you'd like to come to our wedding then please feel free - and I suppose you can bring Potter if you want to, but don't tell anyone else, it's a secret remember. I haven't even told Ted I'm writing this owl to you. Still reply if you want to come - and tell James he can too.
PS - At least I can get rid of the Black name unlike you, poor thing.