Hi Ummm,
Sorry to hear your situation, but it happens alot nowadays. I would firstly suggest you talk to him, on your own, without the kids there. Explain how you feel now and how you think things have changed. Chances are, he hasnt noticed a change or has just become comfortable with how things are now. He may also, on the otherhand, be feeling the same as you, but doesnt know how to approach the subject.
So do talk it over first and see if you can both take steps to 'try again' - give yourselves a time frame to see if it'll work out - say 2 months - if your both still not happy, then it may be best to move on.
If you feel you cant throw all your feelings out directly to him, write them in a letter, and give it to him, let him read it while your there, and onces hes read it, explain why you have written it and what you've wrote down,. Discuss the situation, it may be just a few things that need changing and it could all work out - maybe he just needs a kick up the backside!
If not, then at least you've tried and theres no point in staying if you're not happy.
Which ever direction you choose - good luck
X