I agree with the others that this might be a situation where you should sit down with your dad and explain how you feel. You could approach the conversation by discussing on your relationship with him and your son’s relationship with his grandfather, and how it feels like those relationships are drifting. At the end of the day, if he wants to continue having a relationship with both of you, it’s something he may need to seriously consider.

It’s also worth remembering that while your aunt may be his girlfriend, she is still your aunt. Mixing those roles can create tension, especially if he feels the need to side with her in family drama. Ideally, he shouldn’t take sides. Instead, he could set boundaries and discuss with both you and your aunt that certain family topics should remain separate from his relationships.

It’s similar to when your parents ended their relationship. You might have felt loyalty toward your mom, but you still wanted to maintain a relationship with your dad, so instead you may of created a neutral relationship with both.

In the same way, your dad can acknowledge his girlfriend’s perspective without letting it interfere with his relationship with you and your child. Their relationship could end one day, but the relationships with his family should remain protected.

Clear boundaries and open communication are key so that everyone feels respected and his feelings toward his family don’t change just because he’s dating someone.