My BF says my butt is small…

I’ve always suffered with confidence like literally all my life. My sister is tall, skinny with hazel eyes and literally a model and I’m the opposite and everyone has always made sure I knew that sooooo I became the funny sister instead of the fat short sister… Fast forward to my first relationship, cheated on. Second, third and fourth… also cheated on. Fifth relationship we were together for 10 years but he was addicted to porn and told me I was so gross he couldn’t get it up for me Fast forward to now. My bf and I have been together 5 years and when we met, I was thicker but in the right places. Then we had our son and I struggled to lose it until recently. I lost 40 lbs and my confidence has been the best it’s ever been but since I lost the weight my bf has made comments about my butt. He’s never said ANYTHING negative about my body and tonight for the third time he’s mentioned my doing squats and then got so bold to say I have “no ass now…your butt is smaller. I liked it when it was bigger, I like it now. I liked you when you were bigger, I like you now.” Now my confidence really took a hit and I don’t know what to do. I def don’t feel like I want to doing squats at all because part of me is like 🖕🏽f you man I shouldn’t have to do anything to my body to please you but the other half of me is thinking this is going to effect me a lot more than he thinks - mostly in the bedroom. Side note: he’s gained weight and stuff recently and I have never and would never tell him to start doing crunches because I still love him and his body and don’t need him to change it for me but apparently he dislikes my butt so much he’s given me hints 3 times 🤦🏽‍♀️ Thoughts?