Why does my guy friend text me once a day or longer?

So, we’ve been online friends for 8 years. We’d text/ call all the time when we were teenagers. Met once. I got into a long term relationship w/ somebody and stopped texting him for the last 2-3 years. I texted him near the end of the relationship recently to catch up. It was very slow (2-4 days to reply to each other). After my relationship ended, I was a little more consistent and was able to text him everyday. Since this transition, we’ve been VERY SUBTLY flirting, planning a couple trips/ hangout together and generally getting closer again. However, he is online for only 5 mins a day to reply to me then won’t I won’t hear from him til the next day around the same time, at least. He’d mentioned he had 3 days off recently and he hasn’t texted me that whole time. I’m just interested in getting to know him more and getting that bond again but his unavailability has been making that difficult. He apologized for a late reply a couple times or let me know that he will reply later on but it seems to be a reoccurring thing.
Why does my guy friend text me once a day or longer?
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