I feel I've lost, or am losing, my best friend?

I've known this guy since the start of Middle School when we were both in Year 5. We were both in the same tutor room and on the same desk at the front of the room, and that's how we met. We talked and we got on well and became great friends, before long best friends. We always hung out and played together a lot throughout our four years at the school. We both loved Doctor Who and this would be a regular subject for conversation and games in the playground. He would also regularly come round to mine, and me to his, for sleepovers and so forth.

In Year 9, we both went to the same Upper School as well and we used to hang out in much the same way, though to a much more mature extent, for instance chatting with our friendship group or going to the library together sometimes and doing stuff on the computers.

Unfortunately, he left school after Year 11 to pursue his own ambitions, whilst I stayed at the school into sixth form for the following two years. I was fortunate enough to still have many other close friends that I hung out with throughout my time in sixth form but of course I would never see him quite as many times after that. Throughout sixth form, we would still message each other and meet up, occasionally having a sleepover or campout at his which were always fun. He was doing a course elsewhere in the country at the time. We always talked about the things we used to though, even though we didn't hang out quite as much, due to practicalities, but this was understandable.

Things have changed hugely over the last year and a bit though. When I started university, although we never messaged quite as much at this point, I was having a conversation with him and he mentioned that he was thinking of going away for a while to travel and mentioned some of the countries he was thinking of visiting, one of which was Australia which is what he ultimately went with.

The last time I saw him in person was at a party of a friend's, over a year ago. Unfortunately I couldn't quite have any meaningful interaction with him that night because he got very drunk throughout the party that by the end he was like a mindless zombie. I had originally agreed to stay round at his house that night afterward but because of how 'out of it' he was, I just went home that night instead and I don't think he was really aware of much at all until morning, which becomes an even greater shame when you consider what happens next.

Shortly after this party, he then flew out to Australia by himself for travelling, where he would end up staying for just over a year. He started to drift away from me at this point. It wasn't too bad at the start but the longer he stayed there, the more he changed. His attitude to things and his lifestyle changed, and his home communication just flopped and collapsed. He lived travelling around the Oceanic continent with new friends he met and hung out with over there. He posted pictures of his adventures on Facebook from time to time but that was it. Whenever we talked at this point, I always messaged him first. We could though have good and in-depth conversations when I did strike up a chat but it was a shame that I always had to start it. I was recently told by another friend of mine who also knew him well, that apparently he didn't contact him or any of his friends back home at all, and even didn't contact his own family either while he was away. But the thing that got me the most was what happened after he came back.

At this point it's June 2017 and he's been away for over a year and has already drifted away from me. He mentioned in one of the few conversations we had just months before that he didn't know when he was coming back, but would let me know when. Well, I only found out he had come back after he posted a few things on his Facebook wall which heavily suggested that he was already back, and when I asked another one of my friends, he was able to confirm it because he lived in the same area as him. He never messaged me himself to tell me that he was back, which he said he would. I had, however, really wanted to see him again and catch up. I was still at uni at the time, which is about 100 miles from home, so it's a fair distance. I wanted to see if he would like to come up and stay over so we could have a good catch up. I tried to do it at uni rather than waiting to go home simply because we would be all alone rather than having my parents and sister around and it just suited me better. Also, I knew he wanted to do more travelling, so I literally had no idea how long he might be back for before possibly going away somewhere again, so I just wanted to get it done while he was there.

I messaged him to ask if he wanted to do this. Before I got round to asking, I first just confirmed with him that he was back, and then he said that he'd thought of coming round to my house, but didn't think I was back yet (I don't know how seriously he meant that though as he'd not contacted me about it or anything). I then asked if he'd like to come up to my uni and stay with me there, and said he would and sounded keen to, initially. He said he was seeing a friend elsewhere first, but would come up to see me shortly afterward. It got a little weird after this. Because of his wild lifestyle in Australia for the past year, he told me he would cycle all the way up and it would take him a few days. I quietly thought he was insane by doing this but was humbled that he would make the effort to see me this way. He wasn't clear on times though, so I asked him to let me know when he would come up so I could get ready, to which he just said 'maybe' and added a wink emoji. Then when I responded saying that I would need to know where to meet him, as it's a big place, he just said 'haha' and the conversation ended there. In all honesty, because of his attitude in the latter part of the conversation, I never thought he would actually bother coming up and he didn't. I'm now back home and we haven't talked since. He hasn't messaged me or come round to mine or anything, and I'm wary of asking him to come round to his in case he basically forgets about it, but I also don't want to have to be the one driving everything.

I've just had my birthday as well and he didn't say anything to me then either, not even a small message just to wish me a good day, like he would do in some form without fail every year since I met him. Last year, he messaged me a day late and said he didn't realise it was my birthday (as we were best friends at school, he certainly knew it before). But this year, there was absolutely nothing.

My group of friends here, who also know him, think he's become a bit weird since coming back from Australia. They've seen him walking around topless and with a bandana round his head, like he was in the latter part of his Australia trip, and he doesn't message any of them and I don't think they talk to him much themselves. He also posts long and bizarre paragraphs on his Facebook wall now as well, and he's just made himself a bit of a joke. Whenever someone mentions him now at gatherings, we just laugh and talk about what he's currently like, which is really sad. In short, he's worlds different to how he was in the years I knew him at school.

I'm just bitterly disappointed that he's changed so much that he's almost gone away from me and his other home friends since going travelling and now, because of his completely different personality and attitude, I feel I've lost him. I feel that something might (emphasis on 'might' happen in terms of a meet up if I do something, but it clearly won't if I left it to him and that's not how I think a good and meaningful relationship works. If I'm arranging everything every time, and the one messaging him first every time, I wouldn't feel there's a genuine bond going on between us anymore. What do you think of this situation and do you have any advice on what I can do to try to turn things around? Or is it better that I just move on and hope he comes back at some point? Thanks for all your help!