You already know the answers, look at your own words.
"I know exactly what's wrong with him, same as always has been he wants the best of both worlds, he wants the family life when it suits when he wants us all to go on holiday or on a day out, or someone to eat his Sunday roast with, but he wants to be able to just say fuck off when he wants to"
So why on earth are you putting up with this? Seriously, why? He can only do it because you allow it. You accept his insincere apologies. You continue to see him.
"Bit scary to just think 'he doesn't love me', I'm sure you're probably right but if he felt like that why the bloody hell string me along for all this time, why not just go and find someone he did love."
He does it because it gives him cooked meals, a clean and pleasant home environment and sex on tap. And he has already found someone he loves - himself. Selfish bastards do not need other people to love.
" he knows I have more emotional investment in it so is using that against me."
SO he's manipulative too. 
"I don't want to live together right now because I can't trust him"
If you can't trust him, then why continue this relationship at all?
"The reason I'm so upset also is that he used to do things like this all the time"
So I really cannot understand why you persevered for so long.
" I daren't speak to rl friends and family about things like this because I've found it just comes back to bite me on the arse when I stay with him. Bascially it's well don't moan anymore if you're not going to get rid which is fair enough. So I prefer to vent anonymously atm."
And your real-life friends and family have undoubtedly given you the same advice as on here. Dump him. He will never change. He is not worth the hassle.
As I said, you already know the answer. And if you expect to vent on here and not be told the same as you have already been told in RL, you are very much mistaken. We will not stroke your hair and say "there, there" in a soothing voice. Not while you are still inflicting this man on your son.
If you won't dump him on your own account, then please consider your six year old son. If it infuriates you to be old " fuck off when he [your boyfriend] wants to" , what do you think it does to your son? I think you're underestimating the effect on him. Your boyfriend is encouraging him to call him dad, your son has done so a few times. You really should think long and hard about what's best for your son, and as a clue, someone who behaves like this is not a good person to have in his young life.