Of course you have to resist, but you have to take care of his face. For example, you can say to him: this is not good, I already have a boyfriend, or you can take a few days off to let him know that you don't like it psychologically. If he wants to go further, he is basically allowed. If he is not a good boss, he should know this discretion. If it really doesn't work, then resign. As long as you have the ability, you can still find a good job these days.