These 'Toughen up' comments simply miss the point completely.
I think the reason for the increasingly dark mood is basically probably closer to perfectionism. If you hold yourself to a high standard (setup by having trained with the pace group, although there's nothing wrong with this), then i expect the mentality is: "everything is as i expected why can't i do this?,..., i don't believe i can't keep up with the group after all i trained with them...etc", negative self doubt stylee. Basically if you are an all-or-none, glass-half empty person like myself you will hate the fact that you stopped at all, then as the pace group drifted away the possibility of a perfect race died. Having been in an identical situation, i have to say part of this is down to the fact that the pace makers often have to run faster than actual pace (like at VLM where the 2 pace maker groups from different starts finish miles apart and both ahead of target).
I once collected 6 yrs (i think) of rejections to qualify for a ballot place at VLM. Then on the day they put me at the club start (not red start mass) and the atmosphere was poisonous with all those bald 40-something club runners all intruding my ps. 10 miles in i just got really bored, and bailed. Nothing to do with my fitness or psychology, its just a rubbish event for me. Go shorter, faster, you can do distance in your 70s.
I had PF ages ago and was off for roughly the same time due to it (but then continued to be injured for other reasons). My methods for getting rid of PF were:
1. Rolling a bottle of frozen water (lucozade or coke 500ml bottle, so the elevated part gets right in under the arch,mmmm). This was really easy and felt so good, provides at least short term relief.
2. Religious PF stretches for the whole of the lower leg. I was off work for a while at the time, and so in the day i basically did this 10 min stretching routine at the top of every hour. Also as soon as you get out of bed, when it is most likely to hurt.
3. walk barefoot over sharp stones on the driveway (not gravel, but bigger and sharper). Oddly enough this put the nail in PFs coffin after only a few minutes, maybe it won't work for everyone but its worth a try.
And don't forget to exercise the rest of you in the mean time.