There's that line in Blink about being "rubbish at weddings. Especially my own." I may be inferring too much, but to me that says he's had more than one wedding of his own. If he's continued in that fashion, he may have married both River and Bess, at different times, between Mars and Oodsphere.

Or, if you don't presume monogamy (and River and Bess both don't) he might have married River and Bess in the same wedding.