How long have you felt this way? Is it something that has just surfaced, or have you been feeling this way for a long time? You are correct when you say relationships become "comfortable" after awhile, but that usually means you need to spice it up some. Do something different, go on a get-away weekend, romantic dinner - just the two of you.
You have invested alot of time with this man and you also have two children to think about. He sounds like a stand-up guy, a good husband and father. I don't think I would throw it all away too quickly. Have you talked to him about the way you are feeling? Communication is the key. If you are worried that something you say will hurt him, believe me, it will hurt him more if you're not open and honest with him. And keeping all those feelings bundled up inside is not healthy for you. Besides, if he is doing something to make you feel this way, he can't fix it if he doesn't know what it is. Talk to him.