Hi Lady Jane.
I am with the others here. But I just wanted to emphasise the point that you will not be protected financially if you aren't married. There are plenty of threads here about people splitting and the difference in support between those married and those not is a little scary. Especially if you go on to have children.
The poster who said that marriage is not just a piece of paper was REALLY right. If you give up work to look after children you will be entitled to a share of his pension. Without marriage you won't get anything.
(please correct me if I am wrong, but I believe that is correct. Australia is very different so I may have some of the details wrong) but you should be clear on what you are entitled to.
If he questions it tell him that you can't guarantee that HE won't treat YOU badly in the event of a separation And you need to protect yourself, especially as now he won't commit to you. He seems to be worried about what you will do to him, without considering what he could do to you.
Change your name, a little embarrassment now is nothing compared to what you may go through later. My cousin had to cancel her wedding, when her ex backed out. Embarrassing sure, but now is is married to someone else, has two children and I can't even remember her exs name.
Keep your finances separate and clear. Get a solicitor to draw up documents stating clearly what is yours and what is his.
He may find this harsh, as may you, but it might be the jolt that he needs to understand that you do not feel committed to.
And give the ring back.
Good luck