AITA for throwing away my boyfriend’s "sentimental" college mattress while he was away, now that he’s threatening to sue me?

I (26F) have been living with my boyfriend lets call him "Leo" (27M) in our apartment for six months. Everything was great except for his college mattress. It’s eight years old, deeply sagging, and honestly smells like old sweat no matter what. For three months, I’ve had brutal lower back pain and sleepless nights.

Money isn’t an issue. I offered to buy a premium $1,500 mattress entirely out of my own pocket. Leo completely refused. He claimed he was "deeply sentimental" about it because it got him through his college years and tough times. He called it a "piece of his history." To me, it was a literal biohazard ruining my physical health. Every conversation ended in a screaming match, with him calling me a "spoiled, controlling brat" who wants to sanitize his life.

Last week, Leo went out of town for a four-day bachelor party. By day two, sleeping on our living room sofa, my back pain completely vanished. I realized how insane it was that I was banned from a good night's sleep in my own home over a disgusting piece of foam.

Out of sheer frustration and sleep deprivation, I snapped. I hired a junk removal service to take his mattress to the landfill. Then, I bought a brand-new memory foam mattress, set it up, and made the bed with his favorite clean sheets.

When Leo got home last night, he went to drop his bags in the bedroom and instantly noticed. I expected some anger, but he completely lost it. He started shaking, yelling that I am a "violator of boundaries" and a thief. He accused me of throwing away his comfort zone because I "always have to get my way."

It got worse. He refused to even step foot on the new bed. He packed a suitcase of his clothes, screaming that he doesn't know who I am anymore and that he can't live with someone who destroys his property behind his back. He stormed out to stay at his brother’s house.

This morning, the drama exploded. His brother texted me saying I’m a "psychopath" and that Leo is looking into small claims court to sue me for the value of the mattress and "sentimental damages." My own mother called me crying, saying that while Leo was being ridiculous about an old bed, going behind his back and throwing his belongings in the trash while he was out of town is an unforgivable breach of trust.

He is refusing to take my calls, and his family is entirely backing him up. I know sneaking around was wrong, but I was literally in physical pain every day and he refused to compromise.