My boyfriend (18M) has been acting distant lately, and I'm unsure how to handle it.

We've been together for almost six months now, but lately, he's been acting distant and unresponsive. It feels like he suddenly stopped expressing his affection—no more "I love you" or "I miss you," and his compliments have faded away. When I ask if he’s okay or if he still loves me, he reassures me that he does, but at times it seems like his feelings have changed. He doesn't initiate kisses like he used to, and instead, he just lies in my bed and falls asleep. When I check in on him, he simply says he’s tired. I'm a bit of an overthinker and I tend to need a lot of reassurance. Since I’ve been hearing "I love you" less often, it's really been weighing on me. I want to support him and I’m not ready to walk away, but I’m not sure how to address these feelings.