Should I tell my ex I am leaving?

Boyfriend of 4 years broke up with me a month ago. Naturally I was heartbroken but with some distance and reflection I realise the relationship wasn't working out and it was for the best. I had become dependent on him for my happiness and I was just sleepwalking through life, not really doing what I really wanted to do. I had based my whole life around him and there was resentment that I had given things up and didn't feel like he was putting effort in. He distanced himself more. He wanted to know what it was like to be young and single. We had some horrible arguments in the last 6 months and really looking back we should have ended it sooner, we were just too scared to be alone. I do however have some resentment towards him because he changed so much as a person. I feel a bit hurt he basically dumped me to slut around and go out with his friends. But I do not want to be angry, rationally I know he is perfectly entitled to feel the way he does and he's allowed to want to be single whilst he's young.

Anyway, I sent him 2 of pathetic I miss you, we should be together texts in the first 2 weeks. He replied saying he missed me too however he does not regret his decision and we should not be together right now. He said he wanted to be friends, I said probably not going to happen and plus isn't that just something people say but don't really mean? So I cut him out of my life since then and we haven't spoken. Now I have been offered a job on the other side of the world and I am leaving in 3 weeks. I am very excited and don't know if or when I'll come back to England. This has always been one of my dreams and I was willing to give it up for him which would have been a mistake. I'll be changing my number, and I don't have him on facebook anymore so there's no way he'd be able to contact me.

I am in two minds over whether to send him a message saying I understand why he broke up, I am moving away and just to say goodbye. I don't know whether this would be pathetic. It just seems harsh to just disappear without saying anything. I don't know if I want to slam that door completely shut in his face. I don't hate him and I don't want him to think that. Also part of it is ego, after those texts I'm fairly sure he thinks I'm lying round crying over him. I'll admit part of it is me wanting to show him I'm fine and don't need him. At the same time I don't know if I'll just look pathetic and should just leave it. He was sad I didn't think we could be friends but he said he understood. I think he will never contact me again if I don't contact him first. He is happy to have me walk away from his life forever and never speak again.

Advice?

tl;dr: bf broke up with me, I'm moving away to a different country far far away, probably never see him again, should I message him to say goodbye?

Tell him or you'll always wonder what if...

What if he panics and wants to get back together - will that make your decision to go harder? Is that what you are secretly hoping for? How about writing to him with or without an address once you are already there?