Come on - don't over complicate this - see the situation for what it is. You were dumped - not in a very nice way. He doesn't want to restart the relationship (unless it's to use you for sex perhaps and that's why he's keeping the door open for you - no doubt he know how you feel - will is or is he taking advantage of this situation?). You need to accept he doesn't want you. All you are doing is wasting precious time that could be spent looking for someone else. Think of the emotional energy you are wasting - you're drowning in a sea of unhappy thoughts and feelings - I can only see this damaging you for your next partner - imagine your next partner learning that you spent a year obsessing over your ex - um - I'm going to tell you that would be a very big red flag for me - I'd be thinking twice about wanting to get involved with you. Use your common sense to get this in perspective. What do you think this relationship would be like if it started again anyway - you have already said their were some problems and your aims in life seemed not to align as well they might with the right person. He's already shown you what he is and what he's capable of:-
"My ex ended our relationship 8 months ago, suddenly and without warning."
What kind of person would do that?
"I didn't beg or plead for him to stay but I was (am) devastated."
Well - respect for the way you dealt with that but reflect on the insensitivity shown towards you. Is there a reason why he dumped you suddenly?
"We'd met online and were together for 3 years and, I thought, perfectly suited."
What does together mean? Lived together? Or only saw each other when time allowed? Are you sure he wasn't involved or meeting others during this time? Was he hard to pin down - work commitments always cropping up unexpectedly?
"We're both late 50's for context. It wasn't perfect.. there were lots of issues with moving forwards and some fundamental differences of opinion."
Find someone more compatible - it's the perfect opportunity and you can say hand on heart to your next partner why you split with your ex and didn't get back together - it's perhaps (if you decide to talk about it) a chance to explain what you are really looking for or not looking for.
"I want to travel, my family isn't in the UK, he dumped me a week before we were meant to go on a big trip together,"
If that's factually correct and the complete picture - that's a disgusting way for him to treat you.
"I've behaved very civilly.. he wanted to remain "friends"."
Ask why - why does he want to remain friends? What does he want?
"I've seen him occasionally, he's always responded quickly and politely when I've messaged him but he's never really contacted me to try to get back together."
He's doing a good job of keeping you hanging on isn't he? Why?
"I've tried more online dating but haven't met anyone I'm attracted to and have come to the conclusion that I can't move on while I'm still in love with him Sad"
Well no I disagree - you can fix this immediately in your head by changing your mind. There's no need to drag it out - you can see the score - you know what the situation is - you know what's happened - you must know this relationship is never going to work again. Make a decision to move on and stop thinking about it - think about the future, think about the next person - the net amazing person - the next person who is going to want you and love you and just put your energy into him. You can wake up tomorrow and this misery will all be over imho.
Don't overlook the people you see every day - people you do sport with, work with - ask around - make it clear - I think a lot of people generally like to help connect people - it's great to see people get together.
"So, I think I need to change my thinking and see his flaws."
Well - change your thinking - don't dwell on him and his flaws - honestly - every time thoughts about him and all this come into your head just don't follow that line of thought - it's like watching the traffic outside your window - just stop - turn away from the window and do something more useful.
"As in totally get the ick for him and start to hate him. Am I being totally ridiculous about this?"
As it will inevitably involve thinking about him in some way - even negatively - I think this is totally unhelpful - it's just another side to obsessing about him. Think about the net guy and how you are going to find him and what you want that relationship to be like - invent him, give him a name - Evan - I'm in heaven with Evan - you really have you to clear you head out, remove all these useless thoughts about the past - it's gone. Move on with your life.
"I've tried to be the bigger person, say it's fine and he didn't owe me any explanations, that we're grown ups and both free to do as we please, but as long as I'm idealising him I can't move on."
I don’t know why you keep harping on about how gracious you have been - it's not helped you in any way in this situation has it?
OK you preserve some dignity in one respect but not by clinging pathetically to someone who doesn’t want to be with you and who behaved badly towards you when you broke up.
"Trouble is, I've had a sneaking feeling that he'd come back to me at some point but he's had chances and he hasn't."
Check the calendar - it's been 8 months!
"So if I change my thinking I have to delete this fantasy."
It's nothing as Disney as a fantasy - it's deluded, immature thinking.
"And give up being "friends" with him, as in no friendly hellos (we occasionally see each other at a sport we both do)."
Yes - it's not helping is it (in any way)?
"At this point I'd love to have been happily coupled up with someone else."
So put any time you would have spend obsessing over your ex into obsessing over your next.
"I feel time is moving on and I do want another relationship."
You are probably missing opportunities looking backwards instead of forwards.
"I know it's pathetic but is directed ick a good strategy to get over someone?"
No. Because you are still thinking about them. Don’t think about them at all.
"Indifference would be preferable but I can't be indifferent while I've still got feelings for him."
I disagree. Yes you can.
One day I stopped to re-examine the relationship with my closest musician friend of 20+ years - he's selfish and self-obsessed. I told him this. I still talk to him occasionally - it hasn't affected how I feel about him - I see him for what he is and admire, respect and like him in many ways but he is not what I want in my life - my telling him how I felt really has changed his behaviour towards me - that's fine - I expected it - it doesn't bother me - I'm far happier I said what needed to be said and happier not to have him in my life as much but I'm still fine to see and talk to him - (haven't seen him face to face for 2 years now but still exchange the odd email and fb message) - I wish him well - but he is not the right friend for me - he's not what I want or need - I'm better off without him, happier. The change all came in one moment of reflection, I wrote an email and it was done - my relationship and feelings about him were changed forever.