Dittoing Denise ... don't let him tough it out, his body needs those resources to be going elsewhere right now. If you can help him find drivers (and yes, I know you said he loves driving), make him take the painkillers! It's often the only way to stay sane through this stuff. (And if he's getting gabapentin to work for anything, good for him ... that never did a thing for me but bad side effects ... so at least he has one thing going for him!)
((hugs))

Surgery 5/31/13
Tongue lesion, right side
SCC, HPV+, poorly differentiated
T1N0 based on biopsy and scan
Selective neck dissection 8/27/13, clear nodes
12/2/13 follow-up with concerns
12/3/13 biopsy, surgery, cancer returned
1/8/14 Port installed
PEG installed
Chemo and rads
2/14/14 halfway through carboplatin/taxotere and rads
March '14, Tx done, port out w/ complications, PEG out in June
2017: probable trigeminal neuralgia
Fall 2017: HBOT
Jan 18: oral surgery