OP
You ARE strong enough.
You probably feel you aren't, because you can't imagine your future without him, or at least the man he presented as, before the death of his close relative.
When a catastrophe happens to someone (else eg a car crash) you midget think that they are marvellous for dealing with that situation, and you think that you'd never be as capable as the person it happened to.
It's truly amazing what you can do when "it" happens to you.
Your instinct to survive initially, then to gain strength to actually thrive, is there in you.
It may have been dumbed down by life- people- situations, but you have absolutely got it in you.
If you feel under threat that he might leave you, then quietly get your "ducks in a row", so that you can feel somewhat in control of what happens next.
This should help your confidence even if he does get over himself and values you as his wife, best friend and lover.
I guess you will read all of the replies that us mumsnetters are posting, and you may think that none of us truly understand your situation... that may be true, but surely if the majority of replies that you read are basically saying the same thing, then maybe you should reassess your situation and future and the future of your children.
Lastly, having two young children to care for and to have to make a new plan .. even if it is a just in case scenario, is hard... it'll probably feel insurmountable at first, but as you tick off each aim to achieve in your plan, you'll gain that confidence slowly but surely.
Like working out a new muscle for instance, for a while it hurts like mad, but with practice, that muscle gets easier to work.
I hope you find your courage, strength and confidence, it's there waiting for you to access it.