Why is my (currently long distance) boyfriend shutting everyone out?

I'm quite desperate now. :( My boyfriend of 6 months is currently backpacking through Australia. He left two months ago. I was planning on joining him this summer after saving up enough money. Everything was perfect. But after a while, he stopped saying that he misses me and that he loves me. But he stopped saying "I miss you" to his parents as well, probably some sort of defense mechanism because he doesn't want to seem weak and doesn't want to get homesick. We've been talking every single day and whenever we both had enough time (and a good wifi connection) we Facetimed or skyped. Within the first 6 weeks, he had trouble finding a job, so most days he was bored, which led him to partying excessively EVERY single night. He spent hundreds of dollars on alcohol. Needless to say that I was worried and not really happy about this.

After 6 weeks, he decided to fly to Western Australia, because he FINALLY had a job offer over there. I was happy for him, because he could finally do what he went there for. He was sure he wouldn't be able to party anymore, and since his new hostel is in middle of nowhere, he'd get bored, so we would talk all day after he gets off work. He was sure he was going to hate this place and his job.

However, after his first night at the hostel, everything seemed to change. After his first day of work, he told me how great his new job is and how much fun he's having in this hostel. They're partying every night. They have alcohol en masse, which he pretty much doesn't have to pay for.
Then he hit me with some bad news: he wants to stay for 2 whole years, instead of "just" 10 months, because he's having SO much fun.
Two days later, his behavior towards me started to change. It felt like he was trying to talk me out of coming to Australia? He told me all about the negative sides, like waiting for what feels like forever for my tax file number or needing thousands of dollars on my bank account, just in case I won't be able to find a job right away.

Then things started to get even weirder. He's shutting me out completely now. He doesn't text me anymore, he doesn't send me snaps on snapchat, etc. Just nothing. He's barely online altogether. Of course he can't text me when he's working, but when he gets back from work, he immediately starts drinking.
Whenever I text him, asking about his job or how he's doing he'll just say "good" and whenever I tell him something about my day he'll just be like "haha".

Turns out, he's doing the same to his parents, brothers and close friends back home. He's shutting out everyone who's not in Australia. It's like he doesn't want anything to do with us anymore. Trying to talk to him is pointless, because when he's with his new "friends" (they're pretty much strangers???) he'll even ignore his beloved mother. I've tried not texting him as well. It's been 5 days now and I haven't heard from him.
Whenever his mom texts him, he'll tell her that he's busy.

Two days ago, he started smoking pot and God knows what other drugs. He has NEVER done anything like this before, he was strictly against druge use. His family and I agree on the fact that this hostel is turning him into a completely different person. His new "friends" are a horrible influence.

I don't know what to do. I really don't want to break up with him. We were both sure we're going to spend the rest of our lives together and I truly love him. If he wanted to break up with me, he would have done so by now. If I could fly down there sooner, I would, because I know I could stop him from throwing his future away.
Has anyone ever experienced a similar situation? Does anyone have any advice?