Sorry you're hurting OP. 
I agree with pps - I think someone who is "super-rich" and going for someone in a hugely different social group to them, is probably very aware of the power differential.
Like when someone consciously seeks out someone younger as they are easier to mould?
(I'd say someone in his "peer group", also well-off, maybe not super-loaded but say a surgeon from a rich family, wouldn't have been someone he couldn't have "dropped as easily" as there would be social repercussions).
I'm "vague lower middle class" myself and when I've socialised/dated very affluent types there often is this dynamic.
They can be VERY charming, but there is an unspoken boundary there, especially when it comes to the "things that really matter to them". And yes, their wealth does cushion them from their actions a lot.
I know someone who trained with royals (GOSSIP) and everyone said they were very civilised, very charming, remembered everyone's names....but made very sure they took steps and "kept their actual friendship groups sacrosant".
Maybe if you're working together or were at uni together or are genuinely part of the same social group, the vibe is different, but if you've just met as an older person "in the wilderness" out of context, then I'm not surprised by his behaviour tbh. No accountability.
I also am not sure it would have necessarily been a healthy relationship longer term...you're in quite a vulnerable position with two small kids and feeling the financial strain (absolutely not criticising you for this, the CoL crisis has got everyone down)?
How would the dynamics have worked anyway? Would your kids have been the "poor stepkids" compared to his? Would they have played together, but his having million pound inheritances and yours student loans? Would you have expected him to bring your kids up to his kids standard of living? What if his children resented yours? Would his travel first class and yours in coach?
(obviously it's hurting now, but it could have got worse down the line...just look at the StepParents board!)
Like pps say, I think onwards and upwards is best here. I'd block and forget or leave messages "read and not reply" or whatever works best. You don't want someone who makes you feel the way you are feeling now in your life.
You've had a six month dating experience (hopefully some shagging and good memories) and I really would just chalk to experience and practice self-care and don't get caught up in negative thoughts and "what ifs".
Loads of women have had similar experiences (with rich and poor and middling men) don't let this drag you down or define you. It would have been worse if you had got involved more.
Maybe you can think about steps to improve the financial outlook for you and your children (if you aren't doing this already).