He was unsure at first after a v long search if we'd work out, looking over my shoulder a bit, realised we were really good and meant to delete, then I found out about an issue that had already gone
The thing is, it's wise to not emotionally invest too much too soon. It's sensible to approach a new relationship with a little caution.
There are many ways in which you can do this.
Without continuing to be on dating apps/seek out other people.
Again, I maintain an emotional distance - I don't 'fall in love' easily. But I can do all of that without being disrespectful to the man I am seeing.
It's that whole "Treat someone as you wish to be treated" isn't it?
But this one is less clear cut, he is a good one who screwed up. I'm a good bet too, but I have flaws, which some people - him included it seems - can't tolerate
Yes, of course everyone has flaws. It's a pretty big screw up though, isn't it? Having boundaries and expecting them to be respected isn't a flaw... 
I think it's over, the magic went when I saw the message and I've not got over it. I should have.
I'm not really sure why you see this as a bad thing. I mean, I understand that you are mourning the loss of the future you felt you could have had with him but these are your boundaries. The magic going? That's the barrier coming up because he crossed/ignored your boundary. The saddest thing is that you have spent the last 3 months also trying to cross/ignore your boundary!
Be cross with him for ruining it; be cross with him for not recognising your value and worth; be cross with the friends who think you should ignore your own feelings/relationship expectations... just don't be cross with yourself because you expected the man you were in a relationship with to not be 'looking over your shoulder' at other women at the same time.
Thanks, but I've not really got it all sorted quite yet... but I'm getting there
I'd rather be single that tie myself up in knots explaining away a man's poor treatment of me though. My mum did that after she and my dad divorced. I remember talking to her when she was in her fifties about some concerns I had about the man she'd recently started seeing - I felt that he was rather dismissive of and disrespectful towards her. She cried and told me I didn't know the half of it and that I had no idea the sacrifices she'd had to make just so that she wasn't single.
I made the decision there and then that I would never make such 'sacrifices' myself just so as not to be single.