sorry about your breakup. having a new goal can help, even if a short-term goal. i did my first 50-miler off marathon training, and had a blast. just look at it as a long (long!) easy run, and you'll do great (of course, that depends on the day, the course, etc., so your "mileage may vary"). as for me, i felt great the entire time, and only pushed it for the final five miles; still, i broke the masters course record by more than 15 minutes.
a nice thing about many ultras is that they are very social events; if you're running at more than a conversational pace, particularly in the early miles, you'll crash and burn, so you might as make friends on the trail (or road).
i say go for it -- and keep focused, especially toward the end, or you might trip and knock yourself out, and that'd be no fun at all. another piece of (seemingly unnecessary) advice is to taper, hydrate, and eat well (before and during), and do your best to get a few decent nights' sleep leading up to your race.