Judging by your question, I want to tell you that I think you are such a sweet man. A loving Father.
I am the eldest child of divorced parents, I was 13. While most teenagers were struggling with puberty, and their first crushes, my struggle was with 'why did my Dad have to leave?' It was the hardest thing I ever had to deal with, and at such a early age.
What I understand now, as a grown woman, is that every person has such a unique personality, no one is exactly the same. We each handle problems and heartaches differently, even if two are treated/ or raised the exact same way.
We saw our Dad every weekend, and we had a lot of fun. My sisters and brother were satisfied, we new our Dad loved us so much, but personally, (with my personality) I never felt good about any of it. I didn't want to go home on Sunday night without him. It was a very lonily and sad time for me, sometimes I felt like I was the only one who missed him, and then I remember how that devistation, that feeling of helplessness turned into anger and resentment.
I wish I could give you the perfect advise on how to alleviate all the pain and confusion your divorce will cause, for you, and your kids, but like the other ladies said, all you can really do is be there for them at every oppertunity, always let them know you love them, and kindly/ tacktfully share your feelings with them. But know that you will each handle your pain over this differently. You know Divorce isn't normal, that something went terribly wrong, so don't avoid their questions or their feelings. Don't avoid your own. You talk about your feelings of guilt.. realize that your children may have guilty feelings of their own over this.
I Pray for the the best, for you and your Family. God Bless you.