You are NOT cheating on you dead husband - marriage lasts until death parts us, and you are a comparitively young woman with, I hope and trust, a long life ahead of you.
Falling in love again is quite natural.
I do not necessarily agree with other posters that you must put your children first. To give them a happy life, you need to be if not happy, at least reasonably content-
In my experience love is nearly always a good thing, and feeling loved yourself will make it easier for you to give love.
Try to enjoy being with this new love, without feeling quilty.
How old are your children? Whatever their ages, make it clear that you love them, you still love their father, but you have found a friend whom you also love.