Marathon training should be done in sections. Build a base of fitness, build upon that base, peak near race mileage, taper before your race, and then, finally... race. 

You're going to have off days, and days where you 'just can't' - and that's ok! Sometimes you need extra rest from stress filled training. One (extra) day off won't hurt your entire training.

Even if you're running to lose weight, you still need to fuel your body accordingly. You can still eat (and even eat a lot) just focus on whole, healthy, and real foods. 

You're going to have back to back runs on the weekend. There will be Saturday and Sunday runs, which means there will be Friday & Saturday evening get-togethers that are missed. 

You've earned the ability and the right to train for this! You might as well enjoy each and every single one of those 26.2 miles. Afterall, once you're done, you're a marathoner for life!