You got the part!  Congratulations!

But now you have to figure out how you're gonna juggle that full-time job, the significant other and rehearsals all at the same time.  And don't forget about all those daily mundane tasks like Laundry, Dinner, Exercise, etc.

What is one to do?

You have to plan ahead.  Once you have your rehearsal schedule, take some time to figure out what all will need to be completed before the show opens.  Some things to include:

Time to shop for costume requirements (like underwear, socks or shoes)

Haircut appointments

Vehicle maintenance

Bill Paying

I like to put my whole schedule on the rehearsal schedule that way I have everything in one place.

Today:

Gym 6-7:30am

Work 8:30-5:30pm

Dinner 5:30pm-6pm

Rehearsal 6:30-9:30pm

Desk tasks (paying bills, checking email) 10-11pm

Bed

You have to take into account that you won't have a personal life at all during your final week of rehearsals.  Most rehearsals go "until we're done" which doesn't leave you a lot of time to take care of yourself.  So throughout the rehearsal process, when you find you have extra time - use it to rest up - take a nap, go for a jog, see a movie.  Anything you can do to keep your stress levels low.

Vitamins, plenty of sleep at night and water go a long way towards keeping you healthy.

It's not as taxing as it sounds - you simply have to think ahead and plan for everything that you'll need to do.  And that plan should include the weeks between performances as well - because you're gonna be tired and want to vegg out on the couch.