Hi guys, I need some advice?

I have a friend, I and she have lived together 4 years as we are studying abroad together. We’ve started a new life together and been through a lot of bad and good things together. Even When she need to borrow my money for school fee, I gave the money to her without hesitating. And she also stayed with me for free, I have no problem with that. I also never rush her to pay my money back. She is a good person. She cares about everyone. But her attitude and behavior to me and only me lately is so freaking weird. She seems fine to everyone else. The way she acts like i did something wrong even i didn’t and it’s very different from before. It’s like she doesn’t want to share, talk and make joke and have fun with me as before. Now to me she’s like somebody else and i cant talk normal or make joke and laugh with her anymore. I did talk serious to her but she said it’s ok, nothing happened. I’m so upset. I dont even know what’s happening between us. I don’t know what to do, It makes me so uncomfortable, it’s like i am living with a stranger.