I wouldn't have taken a relationship beyond the 6 month point without meeting his family and close friends certainly wouldn't have moved in!
Have you even met his kids? Then I read not - HUGE red flag!
Also given how little you know about him you cannot possibly know he's not married, has a history of dv or financial irregularity...or even something like paedophilia or rape in his history!
"I know that he had a few failed relationship in the past (the last relationship ended up in a very acrimonious way)" actually you ONLY know what he's told you
You've not only exposed yourself and made yourself vulnerable but also your kids (their being adult age is irrelevant you've made a huge decision that affects them with very little information about this man!)
"I did google him and again couldn’t find anything fishy" he could have changed his name it's not difficult.
Works mainly from home - not in itself suss but with everything else it's concerning
"I’ve found his ex/kids on Facebook and whatever he said seems to be true." How do you know these really are his ex/kids? He could have given you someone else's family details
In your position I'd be moving him out at least until you know much more about him.
"I know that the relationship is still relatively new but he introduced his ex partner to his parents after 8 months" no this is JUST what he's told you, you don't know it's fact
How the FUCK is it your fault? That's bollocks!
Good you're getting rid.
Out of curiosity I'd be doing an image search based on a pic of his rather than using whatever name he's given you.