I am going to recommend a great little book called "The Verbally Abusive Relationship" by Patricia Evans. Withholding communication is a form of verbal abuse, so at first glance, that book might not seem to apply to your situation. I found it incredibly useful, though, in understanding that my marriage was not healthy; that, at the book says "one person cannot create intimacy in a relationship"; and in knowing that it was time to move on. The book can be pretty hard to read if one is not ready to face hard facts about one's relationship. (It was hard for me.)

Here is an excerpt from that book:
Questions that may help you evaluate the quality of your relationship (and whether there is hope for improvement):
--Does your mate enrich your life?
--Does he bring you joy?
--Do you feel a real connection to him?
--Do you think in the same way and share the same dreams?
--Does he show goodwill?

For myself, my answer to all of those was "no". It was really hard to face that but yeah, that is the way it was.

You also asked how to end it. Just be honest with him that you would like to end the relationship. If he asks why, tell him, but don't argue about it. You have needs and they can't be argued away. If he believes you ask too much of him or are overreacting, then it sounds like he doesn't want to be with you either. You can emphasize your desire to do this in a way that doesn't harm the children. Hopefully he can get on board with that. My former husband and I divorced very civilly and are very cooperative today in our co-parenting. Our children our thriving. It is very healthy for them to see that their parents get along.

Good luck.