Does this Golden Prize girl help with the chores like you?

If not, I'd stop being so available for those.

Some -- many -- families (or groups in general) assign roles to people, usually based on whatever the group leader needs to see expressed. I'm guessing the mother gets reflected glory for her son to have such a wonderful prize in this young woman. Her feet could be clay, but because Mom gets such a good feeling from the creating and maintaining this girl as an idol, she's not going to willingly change and all of a sudden recognize you as the gem you are.

If you have not, I would discuss this calmly with your boyfriend, once. I would tell him I needed to feel special, especially by him, and I needed to feel he had my back. If he gives you appropriate reassurances that he loves you and you matter to him, I'd just stop spending so much time with these people. If he can't reassure you that you are important to him, and/or he is not willing for you to spend less time with them it's time to find a new boyfriend.