LSD 18.5m Doubts

Did 18.5m in 5h45min on Sat.

Not a good experience, not even average. Started at 4.45 Am, had to take a restroom break because had started so early, it was very hot and I think we got tired sooner even tho we kept drinking the water. Took a 15 min break at GBs apt to drink water and get a snack. Then she did another 5 miles for a total of 15 and I did 18.64m

Not atall satisfied. Took too long-18minmile, and so tired at the end of it, hurting everywhere.
Very angry with myself. Nobody forced me to start this, and I dont even have to finish it- just put it down as that experience I wanted to have but gave up because it was too hard. Noone has a gun down my throat telling me to do a marathon. But if I want to do it, it has to be a full fledged effort.

Why miss workouts, why eat bad- anyone pushing that 2nd serving of rice down my gullet? Why not wake up at 5 AM to finish the workout because I know I wont be able to do it later. Why miss the XT workouts of yoga nad weights when I know I need a strong core to be able to run better?
Basically why act like an idiot? Who am I doing it for?? Just me. Its only me. So why not put in 100%, heck, even 90% will have me see the finish line.

Really angry today, would kick myself if I could. Lets see how long this frustration lasts. Made worse this morning when read some posts on the prevention site- walkers preparing for a november marathon and can do 10 miles at 13-14min mile. I cant even do a 5K at that pace.Hopping mad.Craazy mad. At me. Have to push myself now. Only 9 weeks left.