The zen master in me wants to put on a soothing voice and say that everything happens for a reason, that we learn from our pasts, and that pain can be a teacher. But let's talk instead about the ways of doing it with class; ways that make it hurt less and leave the door open to friendship. Maybe not right away, but eventually.
Some people need time to warm up to a dog, and you should allow for a bonding period. However if your date is disrespectful to your commitment to your dog, i.e., encourages you to leave him or her alone overnight "because, she'll be ok, it's just one night, or a few more hours," I think this a bad sign.