Family is All We Have
Now this real-life story sounds like it’s from a reality television show and we can’t get over it. The OP got invited to her cousin’s wedding which is great except she’s getting married to the man the OP was engaged to. He cheated on her with the cousin and now they want her at the wedding.
Wait, what? To rub salt into her wound, her aunt kept trying to convince her to go because “family is all we have.” How about thanks, but no thanks? You just have to learn to say no to toxicity no matter where it comes from.