I agree, it's common. I know of a lot of people who either came out later in life having not quite realised before/having not admitted it before, and I also know people who felt their sexuality changed over their lifetime.
I left my ex-husband when I was 30, and we didn't have children, but I certainly found it hard and I really relate to what you say. I missed my ex-husband so much, and in many ways he was a lovely man. I also felt very guilty that I was the one leaving. Our situation was quite complicated, but this is, I think, quite common: many lesbians I know who were married to men found they'd unconsciously gravitated to/attracted men who had other baggage around heterosexual/marital relationships.
I think my experience might be hopeful in a rather weird way! After I left my husband, I dated a bit and ended up with my current partner. We have had what is, on paper, a pretty hard relationship, and in quite a few respects it's absolutely in mumsnet LTB territory. It's definitely not the case that I left my husband and had a fairytale lesbian life, and everything was fine. But, even with all of that, I know so clearly it's right on a deep level. It's amazing to me how different it feels. And I do look back and feel less guilt. My ex-husband really didn't want me to leave and so many people told me I must be kidding myself or just looking for novelty. But I realise now that that relationship would never have been right.
I hope things start to feel better for you. You deserve a relationship that is right for you.