What to do when your unofficial boyfriend [18M] stops messaging you? [22F]

Hello.

BACKGROUND - Zak and I were 'seeing each other' and had been for about two months when all this went down. I had been on several dates with him and was falling for him HARD. He was pretty much everything I wanted. MAJOR PROBLEM - I was also dating other people in the meantime, but he knew this and accepted it since we weren't exclusive.

He'd been saying over the course of the two months how he could see a future with me and even told me he was beginning to love me. Everything was going great. We'd Skype pretty much everyday, and talk all the time - literally all the time. He'd compliment me and even scold me if I said anything negative about our future, for example joking he wouldn't be in it. He was dead sure we'd be together for a long time.

Fast forward to two days ago. He hadn't spoken to me or replied to any messages in a WEEK. I had no idea why, but he was suddenly ignoring me. I felt like a mess, but decided to leave him be after sending a couple of worried texts, because I figured he just obviously didn't wanna speak to me. I decide to spam him on FB when I saw him online and BAM I get a response. I asked him if he still felt for me as I hadn't heard of him in ages and it's not a normal thing to do if you're interested in someone. He says he doesn't want to speak, and to ask his best friend who apparently knew everything.

Well, his best friend tells me (within seconds of me asking - a bit odd) that Zak isn't all that interested in me anymore. He says Zak's confided in him and told him that he doesn't see our relationship going anywhere and he wants to break things off. I begin to cry, etc, etc. I felt heartbroken, upset, and just outright confused. He went from being very sweet and making me feel wanted, to throwing me on the sidewalk and ignoring every one of my messages. It makes me feel sick thinking about how he made me feel before all this.

Few hours later I find out he's met someone else. Now, I'm not an idiot. I am 100% sure it's all because of this new girl. I feel devastated and I don't know what to do. I'm crying all day, and when I'm not, I feel pretty empty - which is strange since our 'relationship' only lasted like two months. But I did see a future with him, and now I feel like I don't know what to do or where I'll end up.

I decided to block him on everything because I really can't be bothered speaking to someone who thought so little of me they couldn't even write me a message explaining how they're feeling. But I still feel sick. It's been two days since I found out and I still find myself tossing and turning, wondering what the hell went wrong and why he just pushed me aside. I'm really hoping this new girl ditches him like he's ditched me, but I know enough about the world to know it doesn't work this way, and he'll probably never get his 'payback'.

I guess I'm asking you guys now, where do I go from here? Thanks.

tl;dr - I was dating a guy who decided to randomly stop messaging me one day after he'd been telling me for two months how he saw a future with me.