Full disclosure, I'm in the same position as your OH and I don't actually see anything wrong in protecting his interests (particularly if he has children, not "baggage").
My OH is intending to move in soon (from to a city from a town). He has children, I do not. We will both be signing an agreement which sets out clearly that all of our existing assets (which include pensions, businesses and my property) will remain our own, with no intention for them to be joint. He will also be paying a token rent which will also cover a share of the bills. This is not a payment towards the mortgage. Our finances will be entirely separate (no joint accounts). Any future assets, to which we both contribute, will be shared. Any individual future assets will remain individual assets. Other expenses (food, holidays etc) will be shared. Any changes to our home would be agreed by both of us but any work that needs doing to the house will be my responsibility. We are both happy with this. We very much view the property as my property but our home.
He also wants to get married at some point (and has asked me) and at the time I said yes. Upon reflection however, I have realised that I don't want to remarry, although I do want us to be together for good. This has nothing to do with finances, it's down to my own views on marriage. I too, want to be with him forever. He is also somewhat sad that (at the moment) it is unlikely that we will be married, but understands my reasons why. I do think that he's the best thing to happen to me, but, with the best will in the world, thinking you'll be together for ever (married or not), doesn't mean it will happen and we both want to protect ourselves.
All of that being said though, this is something that we have both agreed to. I do understand how you would feel let down, since you feel the goalposts have been moved.
If you want to stay with him and respect that he wishes to retain his interest in his property in its entirety, then he cannot expect you to contribute to the general maintenance of the house, for example. He would need to maintain the house in the same way a landlord would, without expecting a contribution from you. I would ensure that you have a clear agreement as to rights and responsibilities and I would definitely make sure that any savings or other assets you have or acquire in the future are clearly defined as yours (in the same way as he expects to retain his).
This is longer than I intended, but just wanted to give a view from someone in a (remarkably!) similar position. If you have the conversation with him (and I would suggest that you have it sooner, rather than later) and you discover that he wants you essentially have the responsibilities of an owner with the rights of a lodger, then you need to reconsider whether that is a relationship that you would be happy with (and personally at that point I'd run for the hills).