Oh Jo - I am so sorry to hear you're having such a bad time.
He is not 'upgrading' - as difficult as it is, please try not to compare yourself to his new gf. He has simply found someone who may be ignoring the red flags and who is in for a rough ride. She currently does not know the pain and difficulties that lie ahead.
But it hurts. I know it hurts. None of this makes you a lesser person.
There is help and support around you, just waiting for you to ask. Financial, emotional, practical - it's all there. Please reach out and do not suffer alone.
We are here always.