disheartening dilemma

[Tri Girl]

I'd just tell him flat out: "I'm riding at a (fill in the blank) mph pace. If you want to ride with me, that's the speed I'm going. If you go too fast, you'll be riding alone. I don't plan on improving to your pace, I don't plan on pushing myself further than I can do, and I won't compromise my body to keep up with you. Period. End of story. This ride is for me and I'm doing it on MY terms."

If he doesn't get the hint he needs to be smacked upside the head.
Don't ride with him if it's going to stress you out. I have done 2 centuries all on my own and a 4 day tour. There were people around me all the time. Some I rode with for a few miles, some I rode with for many miles. You'll find someone at your pace, but most importantly you'll actually enjoy the day and not have to pay for it for days with pain.

My DH is much faster than me. We start out together and he goes on ahead. He usually turns around and comes back to find me and we ride together for a couple miles and then he's off again. Repeat multiple times. It means more mileage for him at his pace, and we're both OK with that. Any good riding partner should respect your own pace. The only way we'll EVER ride together for long distances is if we're on a tandem; and I like my marriage too much to try that divorce maker.