As a French speaker, might I step in? As the word comes from French, I'm assuming that it follows French rules. Therefore Rab has a fiancée, whereas Rab himself is the fiancé, as French takes an extra 'e' to signify femininity. Of course, you might already know this, in which case my apologies. I'll keep my teaching to my job.
[rab] Congrats indeed. I actually think that getting engaged caused me a more dramatic change of lifestyle then either getting married or having children. Now whether that was a change for the better ....