I hope you are feeling better soon. You are obviously in so much pain, both physical and emotional. Was donating your eggs an act to "atone" in some way for feeling like you are a "bad mother"?
Jo, you are not a bad mother. For whatever reason your H has got custody of your children, it is very obvious to me that you went through some temporary lows that affected your parenting. Anyone can see that you love your kids and want so much to mother them. It must be very difficult to bear the loss of your children, and your "complete" family.
While you wrote about you and Andy a few post previously, about him pushing you on the bed and stuff, it just seemed to me that the man was very unstable and arrogant. It seems that Andy is like a drug to you. Just as my H was to me. And we all suffer from the yearning, of course, to be a "successful" mother (father), and have a complete and happy family.
I think you might want to really step back and have a good, long hard look at your exH. And also, to take care of yourself much more, and ask yourself what you really really deserve. To be kept at arms length and dropped the odd crumb? To be hauled along a roller coaster by your fingernails? To be used and then thrown back again when no longer wanted?
Jo, if you lived down the road from me, I would be right there with you now, making you a cuppa and giving you a hug. You deserve so much more than you are getting. But please learn to love yourself more. The rest will follow.