MIL Issues

So I have a horrible relationship with my MIL. Just found out that she recently emailed my husband and told him I’m a toxic human being and a spoiled brat.... none of it’s true. He’s an only child and the relationship my husband has with his mother in completely unhealthy. She is obsessed with him and wants him all to herself. My husband and his parents take summer trips every year. He wants me to go and visit them for a whole week.... I’m like no way I will go for the weekend but spending 7 days with her is enough to make me break out in a panic attack. How do you deal a MIL who wants her son all to herself. I’m at the point of walking away because I’m tired of him always taking her side. Am I in the wrong for not wanting to go that long? He will go out to dinner on occasion with my family but we don’t do weekend getaways or trips with my parents. Oh and by the way his parents just moved out of state and I thought okay at least I can breathe a little bit better... yeah right.... VACATION.....HELP!