What this man is doing is nothing short of a mind screw. He says he's breaking up with you--not for himself--but for you! Obviously you are deeply attached to him and don't want to give him up.
If you really want to keep the relationship, then tell him that it isn't his job to decide what's best for you. That's your job. If you're willing to take what he offers and pass up a chance to marry, then that 's your choice, not his.
I think you are devastated because he is deciding your fate and you are feeling completely out of control. This is infantilizing and infuriating. Speaking of fury, because he is supposedly acting in your best interest and doing what he believes is best for you, this blocks you from feeling angry with him.
After all, how can you be angry with someone who's only trying to be 'good' to you.
Nevertheless, I know you're angry and your buried anger has resurfaced in the form of suicidal thoughts (wanting God to take you). Because you've written to me before, I have the advantage of knowing a bit about your story. If I recall correctly, your entire life has been filled with one form assault or abuse after another.
Unfortunately, when a person has been mistreated from an early age, it's natural to think that suffering is normal, your calling, your lot in life. Because suffering is your middle name, you will gravitate to relationships and situations that continue the abuse. I call this the 'battered child syndrome.'
The fact that you're OK with the crumbs you get, with the fact that he'll never leave his wife, is yet another example of how you don't expect anything good for yourself. I also think that you're caught in a repetition compulsion--which is the unconscious recreation of a childhood wound in an attempt to heal it.
I think that this older married man is like a father to you. If your own father abandoned or mistreated you, then it would make sense that you would choose a lover who would recreate the trauma of your childhood, hoping that you will manage to get your lover to love you the way your father never did.
Because all abused/abandoned children believe that the mistreatment is their fault, this leads a child to think, 'If only I were a better, more loving kid, mommy or daddy would treat me better.' In an attempt to prove how good you are, you will tolerate all kinds of abuse hoping that your parent will notice your pain and suffering and finally reward you with love.
I think that you've always fantasized that one day you would win this man's complete love, perhaps even win him away from his wife. And then and only then would you feel that you've won your father's love. The fact that he's kicking you aside is all the more painful to you because it feels like all hope of rewriting your childhood with a happier ending has been suddenly ripped out from under you.
You are feeling the despair that you felt all throughout your growing up years. Please join a therapy group in your area. I call group, the 'Second Chance Family' because you will have a chance to form attachments to people who will remind you of the people who let you down and this will allow you to safely work through the feelings and heal the wounds.
In the group, you will also be able to experience new and more loving connections and these ties will become the template for your future relationships. Without these kinds of healing attachments, you'll be left with the only alternative that you've been following, which is to allow your unconscious mind to lead you to wrong partners--men who are emotionally identical to the parents who harmed you.
These partners will never be able to give you the kind of healing and loving treatment that you've craved since you were a child; because they are carbon copies of your parent(s) they can't give you any more or any better than your parents did.
This means that you will always be stuck repeating your childhood relationships, with the same tragic outcome. With each failed relationship, you will feel more and more desperate. The only way to break this cycle, is to join a group.
Please follow my recommendation.
I want you to have a good life filled with the love you deserve.