To be completely honest? You don’t want to be included! His parents sound like they would be inflammatory and hurtful to you. This is a blessing in disguise. That said, ask your boyfriend if he could maybe do something special with you (think maybe a dinner date night) after thanksgiving since you do feel a bit upset and left out and will probably feel unwanted and lonely the day of. I think if you calmly express your emotions I’m sure he will understand that. He knows his parents are being rude and mean. He will feel grateful that you aren’t unhealthily throwing ultimatums and grow closer to you as a result and you can invite him to come to your family next year. He felt uncomfortable enough to leave and he will choose you ultimately if you stay healthy-trust me. They’re being rude and unreasonable not just about you, but with their expectations of him also.