'I feel stupid for considering counselling for something I could be sorting myself....'
But you're struggling to sort it yourself (which is ok- get help if you need it.)
As I see it you have 2 things you need to do.
1)Your partner is an arsehole, leave, find somewhere else to live.
2)Don't rush into anything else. You and the OM will both be getting over your previous relationships. You could date- there's no hurry.
'OM is early forties and I am 26.... I thought I'd just drop that and see what anyone had to say. I know it's a large age gap. I have spoken to OM and he is adamant we would be ok, it doesn't bother him.'
Of course it doesn't bother him lol! That age gap is an ego boost for him, and a way of feeling his youth is not in the past. I was in a relationship for many years with that sort of age gap (I was 26 when my then OH was 40.)
If you were to be with him, or worse still move in with him (It's a trap! Don't do it, at least not yet.) you would soon notice the significance of the age gap, because the glamour of the unattainable would no longer be there.
You might notice things like other people your age are still going out and having a laugh etc, whereas if he goes out clubbing, he looks really lame unfortunately. You might realize you don't find this middle aged man as attractive anymore. You could find he pressures you sexually, because part of what he wanted from you is the sexual excitement he wasn't getting at home. He will probably want some things that are more sedate than you would like them, such as a nice view rather than a city break (these are just a few possible examples and yours might be completely different.)
Also, you will be watching someone die- they will grow old, become even more unattractive, get ill and die before you. You don't have to have that, you can find someone your own age and grow old together rather than be a fairly young widow. When I was 20, I was really into a guy I got off with who was 18 years older than me. He wasn't as keen as me. He said to me 'do you want to watch someone lose their looks, get old, die?' or something like that. Of course it happens to us all, but some of us are further along the journey than others. I found out a couple of years ago he died of a stroke at about 56. I would've been left a widow at 38. Something to think about xx