Now that same-sex couples can marry, I think civil partnerships are obsolete and also a bit rubbish. They were originally a mealy-mouthed way of getting round the fact that the statue books defined a marriage as being between one man and one woman. And now you can get situations like OP's, where there's a sense she's being denied the full monty of marriage. You can't call yourself a spouse, legally, only a civil partner, and legally you're not married, so what are you, civil partner-shipped? It's just dumb. Then there's the fact that if you move abroad, many other countries won't recognise it. I don't think I'd have much patience with the whole CP thing myself. You can have a civil wedding if you're not religious.
About this man in particular, his proposing a CP is a red flag that he's avoidant or ambivalent. He may be a perfectly great person, but that doesn't necessarily mean that he's a good life partner. There are so, so many people out there who are ambivalent about attachment, and it's thoroughly miserable being tied to one of those. Ask me how I know. Accept him if you want to spend half your life being rudely pushed away, in one way or another.
Then there's the man's handling of his son. Not cool.
OP, he may be a good person, he may make you laugh, you may fancy him, you may have a great relationship with him, but none of this necessarily makes him a suitable person to be legally shackled to for a lifetime. What it does is make him a good boyfriend. For marriage - forget this CP nonsense - you want someone who is REALLY stable, knows what they want, and does not have any hang-ups about commitment.
Tread very carefully with someone who has commitment issues. They're not fun, they're not cute, and they shouldn't be your challenge to overcome. Don't fall into the trap of thinking that if only you were cleverer/richer/prettier/whatever he would propose marriage. This is about him, and nothing you could ever be can change that.
Love,
The Booming Voice of Experience