Divorce and my children

I am unfaltering in my love for my children which is why I will go to the grave regretting not being able to love their mother anymore.
I am extremely happy with my new partner and we are planning to have children of our own but that does not reduce my regret over my failed marriage. Had children not been involved then I would not have given the break-up a second thought. It would have been sad, it would have been hurtful but it would have been over.
Children have the obvious effect of prolonging a failed relationship for many years and that brings issues. My ex and I get on well, better than most I'd say but that does not ease the pain of my hurt children. Evidently my upbringing has allowed my hurt to continue long after the actual breakdown of marital happiness.
I'd like to consider that as a recently turned forty year old I am sufficiently modern thinking to realise that marriage is not the sanctity it once was and that the all too common break up is sadly inevitable but still something inside me fights against modern thought.
I believe that children should be raised within matrimonial surroundings and that parents should endure for the love of their offspring but life just doesn't work that way these days.
My 13 year old daughter has some grasp of what reeality means where relationships are concerned but with my 3 year old son it is different. I sometimes lay beside him when he sleeps and I apologise every single day for not allowing him to know what it is like to grow up in a "normal" family environment having mummy and daddy there 24 hours a day. I could quite easily shed tears over this and if thoughts are left unchecked I usually do.
I know that he is well cared for and loved not only by my ex and I but the two others that have filled the gaps left vacant after the split so why am I so concerned and upset?
I obviously believe in the family values but am not strong enough to sacrifice my life for the sake of them. My ex and I could easily have plodded along for twenty years or so not really enjoying life but merely living it. We could have lived with limited passion and diminished love and we'd always have the daily conversation regarding how our children were doing but little else to stimulate.
Should that be enough...yes it should! Was it enough...no it wasn't!
I expect to hate myself forever or at least until the day that my son can sit me down and say, "It's okay Dad, it all turned out okay in the end."
I look forward to that day in the hope that he can say it and it hasn't mattered.