Have you considered seeking marital counseling? If nothing else is working out and you are far beyond the avenue of discussing things between yourself then you need a third person's intervention to put things in perspective for you. A counselor can help restore your relationship with your spouse and if it is meant for ending, you would still gain a lot of strength and insights into how to pick up the pieces and restart your life. A therapist is your best resort if everything else has failed.
It’s not a new situation that just happened. She always expressed need for more connection but I focused on everything else in life and just stayed happy that she was there. I never tried the way I should have and left her needs on the back burner. She isn’t leaving the kids. She wants us to split because she hasn’t gotten what she needs from me and has waited for so long that she’s finally just detached. I had plenty of chances to change and never did. It’s totally my fault.
This is really a depressing situation. you must ask her the reasons why she wants to leave her family with 3 kids. How will they live without her. Question her for the things form which she is emotionally attached. tell her atleast you deserve to knoww the reson for her leave and sort things out accordingly.