Smoothie, guilt is so pointless. There's no need to feel guilty for either of those reasons. if you got into a relationship it would likely be ages before your kids knew, and your ex-h actually left so that he could see other people. Therefore what are you meant to do? Not becoming a nun, that's for sure, and your ex-h isn't concerned about still being married and having left to persue... whatever so why should you be?
As for whether it's too soon or not, you won't know til you've tried, maybe a few times.
I thought I was ready about 6 months after leaving my marriage, but from about a week before I left right to this present day, I've never shed a single tear over it. There was only utter joy at being free! All my grieving was done while I still lived there and faced that I was flogging a dead horse. I dated about a month after leaving but only on a FWB search. It was fine and suited me. I got into a relationship at the 6 month point and swiftly exited that relationship having realised I really wasn't ready at all.
After the big bad break up last year, after my last longish term relationship, I was ready pretty much immediately, truly ready. But although I dated nothing really happened (apart from a very short relationship with a complete unsuitable) and then there was this sudden and massive shift in my thinking and attitude and I went back to totally not being ready at all. Hence the non committed LDR thing with BC being pretty much perfect for me. So yeah I really think sometimes you don't know til you try. And there's no harm in trying :o