some guys just can’t have enough options in their back pocket, it helps them to treat their partner with disrespect as they always have another option or three in case they get called out. You almost definitely deserve better than this, just walk away.
I think he likes the attention you give him and feeling wanted. I also think he invites you to spend time with him to make public dinners go more smoothly. He doesn’t want to make dinners with his dad and yours be weird, so he’s nice and friendly in person. And yeah, he doesn’t want to be the bad guy. You need to stop trying to interpret his “signs” and start doing your damnedest to get over him.
Little tip- probably best to stay away from your parent’s friend’s kids. Obviously, that can get messy.