Advice Please

Okay so I need some advice! So my boyfriend (18) has been kinda weird lately, I only see him about once a week and we only ever really fuck. We talk a lot about what we’re gonna do when we graduate and how we’re gonna be together but it’s been kinda weird lately. He works every day and he doesn’t drive so it gets really hard to see him. His sister is my best friend so she’s been trying to tell me that he’s just really bummed lately but it’s been really awkward. I don’t really know what to do I love him immensely and idk how to handle it what should I do?