What are some ways I, a 23-year-old man, can encourage my 22-year-old girlfriend to express whether she is still interested in me?

**Context:** This is my first relationship, and we’ve been together for 13 months. For the first six months, everything was wonderful. She would express her desire to spend time with me, share how much she missed and appreciated me, and our time together was fulfilling, including our sex life. However, things changed after we went on a week-long road trip at the end of summer. Since March 12, 2025, we haven’t been intimate since October 2024. When I ask her how she feels about our time together, her responses are usually just "good" or "okay." She seems unhappy whenever we're together. When I inquire if something is bothering her, she simply replies with "okay." If I ask if I've done something wrong, I just get "nothing, it’s okay." I’ve initiated conversations about strengthening our sex life, but she shifts the topic. I express my appreciation for her, yet we remain at a "good" level. It seems like she may be dealing with some personal issues, but despite my reassurances that she can talk to me about anything, she hasn’t opened up. We live close by, but since our plans were canceled today, we haven’t seen each other in two weeks. Frankly, I’m growing weary of only receiving brief, uninspired texts from her. I'm uncertain how to encourage her to share her thoughts with me. I strive to be as respectful and open as possible, yet she continues to disregard or deflect my efforts to connect. I genuinely want this relationship to succeed, but I can’t shake the feeling that she might not be invested in continuing. How can I encourage her to open up?