What to do on a Sunday night
 

I am bringing my Father and my Aunt to see Celtic Thunder tomorrow night. But I need to figure out how to entertain myself for 3 hours while they are in there. I can walk around if the rain holds off, but it is sounding like we will be getting some storms then. So I need to find a place (besides a bar - don't really drink) to hang out for three hours.

Well, most obvious is the AMC theatre that's near the Orpheum, in case there are any movies you've been itching to watch.

Or perhaps catch a show of your own at the Wilbur, Cutler, Opera House, etc. Other than that, I'm not sure what other options you have aside from the usual things that people do on an evening after museums are closed: dinner, bar (which you already nixed), enjoy the scenery/outdoors (which may not be doable due to weather), or entertainment (shows, movie, club).

Luckily it didn't rain. Ended up sitting under the ICA, they had some somewhat comfortable chairs set up there for the cafe. Unfortunately with all the new buildings, not much left of a view from there.