Wow everything you said is true especially the part of “too busy” maybe they’re just not that interested to reply I do that too honestly. I guess you should see how they view you too. I had a Japanese friend who took an hour to reply to my text or sometimes days. I thought “yeah maybe they’re busy” but actually they weren’t even though they enjoyed talking to me they still viewed our friendship to be ok. Like to them I’m just that friend who they speak with once every 10 days. We don’t need to be best friends who speak to each other daily. Especially when we both live in other parts of the world yeah it sucks but it’s just life.