Good morning L10, you're in a bit of a pickle, torn between emotional worries & concerns & the practical side of things.
I think you need to see a solicitor soon to help you untangle the practical side of your life & property.
My initial thoughts were that it might be unwise to burn your boats too soon regarding your right to your matrimonial home. Take advice about what can be done to ensure you retain some rights over it in the event of sale or death of your ex. Why should you give all that up after so many years together?
Furthermore, re-marriage has so many legal ramifications I would be careful of that commitment too! If yr new husband promises to take care of you on his demise, how do you know his children won't be aggrieved that their "step mother" gets their hoped for inheritance & make life very difficult for you, legally & in general? I would be very very careful which is why legally you need to know your best options.
After so many years with your ex it's only natural that you still care for him. After all he is the father of your children & to be respected for that. However, if your emotional tie to him is getting in the way of your new relationship, perhaps marriage, however lovely that seems, is not the way to go.
Think of your future when perhaps you are not so mobile or become ill. Do not give up what you are entitled to for the sake of a clean break. Whilst you're still married you have rights & if your ex died tomorrow, those rights potentially could kick in. Take legal advice!