It's not polite to refuse an invitation from your partner.
Jim's girlfriend invites him to come have dinner with her and her family.
Jim wants to let his girlfriend know if he's coming for dinner with her family.
Jim accepts his girlfriend's invitation to have dinner with her family.
Jim says he won't go to dinner with her and her family because he would be uncomfortable.
Jim's girlfriend feels closer to him because he's willing to spend time visiting with her family.
Jim's girlfriend is insulted that he won't come and spend some time with her family.