Mixed feelings?

I don’t really know how to properly explain this feeling. I’ve been seeing/dating a guy for the past 3 months (We’ve been talking for about 5-6 months now) & we haven’t made anything official yet. I’m really attracted to him & initially had more intense feelings for him. 3 months later, I still feel the attraction when I’m with him in person, (we see each other at least once a week bc of distance issues), so when I see him in person I’m all over him. Our sex life is great & we vibe really well & I know I have feelings for him but the moment he leaves, it feels like the feelings vanished. It feels like nothing... I don’t know how to explain it... I just don’t feel anything when he leaves, but when he’s here I can feel all the emotions & we vibe well & I’m all over him. He doesn’t really express his emotions and feelings for me that often so maybe I feel like he’s not into it that deep even though he says he is? I don’t get what’s going on, I just need to hear from an outside perspective.