<human>: My family and I will be going to an amusement park tomorrow and my SO decided to ask my cousin to go. My cousin is 20M and has a history of ruining family trips because he is very disrespectful to his mother.

For some back story, he has been MIA for a little over a year now. He has decided that he would rather get high and sell dope than participate in life. His mother is always expressing to me how sad she is about his life choices and that he never responds to her calls/texts or comes to see her. After my SO decided to invite him, my aunt is now excited to see her son.

I have never been to a family function with him that didn't end with my aunt upset, pouting, wanting to leave, and ruining everyone else's fun. My SO absolutely adores my cousin for some reason and thinks he is super fun to hang around. I cannot stand my cousin. 

We are dropping a large amount of money on this trip and I'm already feeling like it will be ruined. I don't know what to do about this situation at all. If we hadn't already paid so much money for our tickets I would stay home. Also, because my cousin is going, the option to carpool is off of the table and we will have to drive our own vehicle, which will end up costing us even more money (the drive is 200 miles round-trip)

How should I even approach this? I'm frustrated beyond belief that the family party pooper is now attending. I already know my aunt will be extremely upset the entire trip, and my SO will more than likely ditch me with my aunt so that he can hangout with my cousin.

Can you succinctly summarize the text in 1-3 sentences?
<bot>: My cousin has a history of ruining family get togethers and was invited to come. I'm afraid our family trip is now ruined and will no longer be any fun.