Oh my heart aches for you. I too have three boys, older than yours, but when they lost their dad in 2016, probably similar ages.
Be kind to yourself. That means don't judge your feelings and actions. Know that the dating thing can take a long time.
For me, it took ages. Being a female and labelled as "writer" (which men, I think, assumed "no money") and my mop of terrifyingly white hair... ah, it was all so slow. But someone truly amazing showed up... eventually.
Sounds like you had a very good marriage, too. That's a gift! But it'll set your bar high--as should be!
Somewhere there's a woman who loves boys of all ages, and she'll be just right! I so wish you the very best. Sorry if this is just too personal. But your words just hit me: I know.
Nothing good is easy.