I have an 18 month old. I've had to do it a couple of times now. It's not fun. At all. There were tears, but not on her end at all. I think the key is to leave him with someone you trust. In my case, Facetime (video chatting) was really fun for us. I still felt like I had seen her, interacted with her and that she had the reinforcement of seeing me and feeling (hopefully) loved and supported by me.
As for the nursing part, I have no idea. We were all done with that when I had to leave. Will he take a bottle from someone else? If not, I'd definitely start working on that now.
As for you, KEEP YOURSELF BUSY. My breakdown came when I was alone in my hotel room. You have too much time to think about how much you miss him/her.
All the best to you. It will be over before you know it.