The prince didn't want to be there and was appalled by what was going on, but was powerless to stop it, this eventually changes when he has enough and decides to lead a slave revolt against his father and the other princes of his kingdom to free the beastmen, eventually leading to him being the king and banning beastman slavery and attacks, this is after both kingdoms have fallen to ruin however (lerunda's country falls into civil war after it's discovered alice isn't the miko), from the spoilers i've read, the kid is trying to fix relations with the beastmen around the continent and get on good terms with lerunda and gaius, but considering gaius's dad was murdered by a group of soldiers he was technically leading (forcefully mind you), this is not easy, and no the prince is not a love interest of lerunda's, if i remember right he's engaged to the princess of the kingdom that has lerunda's sister as a miko