How much importanc to whom? Any idea/ suggestions?

no matter, how demanding she is, She is your mother. Talk to her, and listen to what she is afraid of. There has to be a reason(logical or illogical) for her behavior. It can be difficult but not impossible, i'm sure if you will talk to her, things would go better. After all you know her better. Right! Don't think about leaving one for another. Think and act positively.

I think this is a very serious issue and I believe you are in a stressful situation right now. For your first question, we are supposed to respect our parents and listen to what they tell us. But our actions do not have to always conform to their liking and decisions. God gave each one of us the ability to discern the right and wrong actions and He also gave us the freedom and free will. We are personally responsible of our actions, happiness and sorrows. Next, for your relationship problem, I believe you've got to do a lot of adjustment and coaxing to your mother. But you don't have to give up your own happiness just to please and obey her. I guess you should assure her that you won't leave her just because you have a romantic partner already. More so, if you're planning to get married; it is natural for a mom to feel being left out specially in your case that she has just been widowed. It is best to talk this over with your partner, too. You could suggest arrangements regarding your widowed mother on either to tag her along in you and your spouse's own house (if you're planning to tie the knot) or other measures which is advantageous to both parties. I hope you'll be able to make both parties agreeable and change the wrong notion of your mom. Take care and God bless.