Talking on the phone for 4-5 hours at a time, what is going on (we're both in mid-30s)?

I met him on a language exchange app and been talking for about 4 months. He's Japanese and I'm Latina. I help him with English and he helps me with his native language. He is highly intelligent, and I am multilingual. We somehow end up talking for hours and I feel if we had no work we'd talk more. It is never ever flirty, only about experiences, life, history, language, society... He seems to enjoy the talks and we laugh a lot, like hysterically! I started developing a very strong crush... but he had mention that he wasn't interested in having friends and wanted to be alone (he told me he is a-romantic and a-sexual but he said he wasn't entirely sure). The reason for the latter has to do I think with some terrible experiences in his life... but I am struggling! I thought of stopping our talks but I love them and learn a lot. I enjoy his laugh.

Talking on the phone for 4-5 hours at a time, what is going on (we're both in mid-30s)?
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