I would think that what’s wrong with you is that you’re just not a fanatic about riding a bike. As for the stamina and endurance issues, I would think those are matters of training yourself. Personally I think you’re crazy if you allow your vacations to revert to torture sessions. If you’re not into cycling to the extent of your boo’s family, let them pedal their frenetic asses off as you uber or lyft to their destinations while enjoying and photographing the scenery. Tell boo that you’ve tried it his way, and that perhaps he could cancel say one in 4 bike excursions to ride with you in comfort to wherever the group is biking. So the choice is either to dedicate yourself to living on a bicycle til you can keep pace or saying “screw it. It’s my vacation too.”