OP you need to be much more worried about your financial vulnerability than whether you partner is insulting you by not proposing.
You seem to have been drifting very passively in this situation and you really need to take control now.
How old is your youngest child? If they are very little, focus on organising some childcare so you can get your skills up to date/get training etc, and get your CV in order. There are some courses for helping women get back to work. Start doing even a days paid work ASAP (by Spring) so you start to build a CV.
If your child is at school then please do the above but get into a PT role ASAP. Clearly this will involve some negotiation on childcare with your partner, but it is high time you started to assert yourself.
In terms of your (frighteningly) vulnerable situation, start by going to citizens advice to find out what rights you would have in the event of a split.
Separate to that, if you want to get married, tell your partner this, and set plans in place for summer. Give him limited options as you go (July or August, this venue or that) - if he’s been with you for 18 years, he clearly wants to be with you, just isn’t bothered about marriage - so you need to motor it along, rather than waiting to be asked.
As someone said above, in the nicest possible way - you have been a bloody idiot. We don’t live in the Regency as Bridgerton - so please stop behaving like a powerless 18 century woman and take some control.