My long-distance girlfriend (25F) has been behaving differently lately.

I've been in a relationship with my girlfriend for five years now. We've had a wonderful connection, getting along really well with hardly any arguments. About three years in, I received a job offer six hours away that I couldn't pass up. After discussing it, I decided to take the job, and three months later, she moved in with me. We had a few minor adjustments but overall, things were great. A year later, she expressed that she wanted to move back home to finish her studies. I was a bit disappointed but supported her decision. At first, everything seemed fine; we talked daily and visited whenever we could. However, lately, I've noticed a significant change. She takes a long time to respond to messages, we rarely talk on the phone, and it feels like her personality has shifted. She seems more extroverted now, which is difficult for me to understand. I truly care for her and want to marry her, but I can't shake off these feelings. She hasn't given me any reason to suspect she's unfaithful—there are still photos of us together on her social media. I'm confused about what to do. Should I share how I'm feeling, or might that come off as accusatory? Is this a normal phase in a long-distance relationship? Any advice would be greatly appreciated. TL;DR: My long-distance girlfriend is acting differently, and I’m unsure how to address it.