For what’s it’s worth the logical part of my brain says there isn’t anything going on but at the same time I have been burnt so many times on the trust front that it’s hard to be logical.
What struck me is that you are living with a liar, so your constant mistrust is perfectly logical and rational. It doesn't matter whether anything is "going on" or not - the problem is that so long as you stay with him you will never really know what he is up to, and certainly not what he's doing when he thinks you wont find out.
He said it’s what blokes do and to stop being irrational
It's what some blokes do. Blokes like him. You could find a much nicer bloke?
I was 19 with a very small baby and really wanted to believe it was just a one off mistake and lapse of judgement
And now you are older and wiser. Liars rely on us believing what we want to believe. They tell us what we want to believe instead of the the truth. And so long as there could be a even smidgen of doubt we believe them because we want to, or need to, and we gradually accept smaller and smaller smidgens of doubt and more and more lies. And that's how they get away with it. You wanted to believe it's a one off but now you know for sure that it isn't. It's part of a pattern of dishonesty and disrespect.
he has persistently lied about all sorts of things which has made it hard to build trust.
It's not rational to trust a persistent liar. What he says to other people when he thinks you can't hear is a more reliable indicator than what he say to you.
I don’t want to be a jealous or controlling person I really don’t.
Jealosuy is the healthy reaction to someone stomping all over your boundaries.
I want to have the level of confidence he has about himself and our relationship
And so you should - what he is says is how people feel in normal good relationships,
where he has said several times he never doubts my feelings for him or feels jealous or worried when I get a lot of attention from other men as he knows I’m not even vaguely interested.
But he's probably lying about that too. He probably does feel insecure about you, because liars and cheats don't really trust other people. They think everyone is like them.
You can't have the realtionship you want with him. You could have it with someone else, though. You're a nice trustworthy person, you deserve a nice trustworthy partner.