Thanks for the chapter!
Somehow I get the feeling that the princess and head priest are very corrupt, lying about more than a few things in their story of woe, and just looking for war potential. As for why MC didn't return home I'd say the likely reason was the return jewel is a fake and just teleported him somewhere else in the world at random with the only set condition being far away from the kingdom. After all, if needed the princess' power to summon someone from another world, then would need it or an equal power to send him back. Otherwise why didn't the priest offer to do a summon in place of the princess who was tired out? Also, considering they locked him up, gave him terrible food, and never saw the princess since other hero was summoned I'd say the chances of them going through the effort, materials, and magic to send him home despite having kidnapped him and requested his help in a fight he had nothing to do with wouldn't be nil, but in the negatives.