Why isn’t he replying?

I have been friends with a guy for about 2 years now. He recently confessed his love towards me and whatnot and so I have given him a chance. But we are in different countries with very different time zones. He is a busy person. But he has just stopped replying it’s been 4-5 days now. I’m so worried I keep calling and messaging him idk what to do anymore it’s hard because he’s in the UK i’m in Australia. We have not gotten in any argument whatsoever everything was very chill between us like he’s not even active on any social media or opening my messages.