This is one of those rare occasions where really you don't have a good enough reason to leave...not yet.
Those things you think you've missed out on you can mostly achieve with your dh.
It's also unfair and unrealistic as pp have said to expect one person to completely fulfil you.
What about your crush drew you in? If you say maybe we can help give you perspective on that.
How old are you? "Late 30's" It's not just men that have mid life wobbles. Approaching 40 can hit women in the ego too! It can make them act just as stupidly, thoughtlessly & selfishly as the arse that dumps his wife & kids for a 20 something gold digger.
"Biological last chance saloon to pro-create..." This too.
When did your mum die? Many reevaluate their lives in grief - but there's a reason experts in bereavement advise not to make major decisions in the immediate aftermath of a loss. And "immediate aftermath" the time of this differs for everyone.
Have you had any counselling? Not couples counselling just for you. You need to reset and focus on what you DO love about your dh and your marriage and a good relationship therapist can help you do that.
The man who's seen you give birth, hungover, throwing up, no make up, unwashed etc and you've seen him that way won't seem as 'novel' or 'exciting' as mr new sex who simply hasn't had that experience of you yet.
I'm 46, I've been single almost 16 years, it suits me... I cannot see it suiting you, you'll lurch from one unsuitable guy to another seeking excitement (which usually comes with narcissistic, abusive, irresponsible...)
As pp I've seen it before, know what usually happens? They end up miserable, regretting their mistake...meanwhile the husband they rejected, who was a good man has been snapped up by someone far more sensible, less immature and more realistic. I've even seen the wives who left trying (pathetically really) to seduce the ex they left away from their new lady or at lest making it look like they have. It's backfired in every case, in one I know so spectacularly that now he's DC won't speak to her.
In short? Grow up, get some therapy, if you want a better relationship you have to put the work in.