All done. How to explain?

I have just found this site and other information on marriage and adult ADHD and I can't believe how much rings true to my own experience over the last 9 years.  I've been married for almost 8 years, and have two fantastic daughters, ages 2 and 4.  After (what seems like a fairly typical!) whirlwind romance and honeymoon phase of the first couple years of marriage I've been struggling since the birth of our first daughter with how much I feel like my husband has put the bulk of his time and energy (and money and space) into all kids of external projects, and not nearly enough into our family.  It has been frustrating, disheartening and disappointing to feel like I need to drag him away from other things to give me and the kids the time and attention we want and deserve.  After discovering that for the last 3 years he has been seeking women on dating, affair and hook-up sights (even though he swears nothing in person has ever happened and he's never cheated, he just called it "flirting") I am all done, we are living separately and moving forward with divorce.  I know it's the right decision emotionally and financially for me and I already feel relief even though I only made the decision 6 weeks ago.

My hope is that my husband can be a good co-parent and find his happiness eventually, but I know it couldn't be with me.  My own personality has changed with parenthood, and I think has been much more severe as a reaction to my struggles with him: I want to be able to live planfully, focusing on my kids, in a house and yard that is clean and not overloaded with stuff, spending responsibly, and not being the only one who manages all the "stuff" that has to get done and just comes with adulthood.

My challenge is my husband- he is so bewildered and blindsided and confused.  I care about him and want him to be able to get through this and find happiness on the other side, and I NEED him to be able to work with me on helping our kids make this transition, and to be a co-parent, even if it's not in the way we both expected but he just cannot understand why in the world I would do this.  He wants to know if someone is telling me what to do and say.  He wants to know if the reason I don't love him anymore and haven't been attracted to him (both not true, I just gave up trying to make him show like HE was interested) is because I don't like men in general.

He does not understand the huge inequity in time - both the fun bonding times and the hard work of parenting times!- spent with the kids, he does not understand that I detached myself emotionally to protect myself, he doesn't see that I didn't get any of the partnership in being a family that I wanted/needed and didn't feel like a partner as he let time and money spent on other things always go way beyond what we agreed upon.  And yes!  I've tried over the years to explain many times how I felt.

So . .  I would love advice on HOW I can explain this to him in a way that he may understand, while minimizing hurt.  I feel I've BEEN trying to explain all those frustrations, and it just doesn't sink in (see "maybe she's a lesbian theory).  ADHD is not on his radar, my therapist actually brought up the possibility. I don't think he'd react well to me suggesting it, but can I help him understand that he had a hand in what went wrong and maybe be able to understand so he can start to move on?

Thanks so much, I've found the people on this forum to be very kind and helpful and I now know I'm not alone!!!