My roommate’s partner has basically moved into our small apartment for free

I rent a two-bedroom apartment with my close friend, Sarah. We signed a strict lease agreement that explicitly states guests can stay for a maximum of three consecutive nights. Three months ago, Sarah started dating a guy named Dan. At first, he would just stay over on weekends, which was totally fine.

But over the last six weeks, Dan has basically moved in. He has his own keys, his clothes are taking over our shared laundry bins, and he spends all day sitting on our living room couch watching TV while working remotely.

Our utility and electricity bills have literally doubled, and the apartment constantly smells like his takeout food.

When I brought up the utility bill to Sarah and suggested Dan needs to contribute 1/3 of the rent, she got incredibly offended. She claimed he still pays rent at his own place, that he’s just "spending time with his girlfriend," and that I’m being hostile and greedy.

Dan hasn't offered a single dollar for groceries or bills, and yesterday I found out he used my personal expensive coffee pods without asking. I feel like a stranger in the apartment I pay half for, and our friendship is completely deteriorating over this. How do I handle this without causing a massive blowout?