How should I get back in touch with him?

I met a really nice guy while I was playing an online game and we became very good friends.the thing is I stopped playing almost a month ago because I was very busy and promised I’ll add him in my messenger list,which I wasn’t able to do,as I was busy with other stuff.he couldn’t add me because I didn’t give him my ID.so we lost contact since then and I really regret it.I bet his level is way higher then mines now(in the game) so I guess I won’t be able to spend time with him there.plus I already made a new character and he doesn’t know that.I will send him some private messages telling him I want to get back in touch,but don’t really know what to say.how can I explain the way I left so suddenly?how can I ask him if he wants to remain friends,if not in the game,then at least we could talk on messenger?it’s been a long time since we last talked and I dunno from where to start.