Your relationship with your children will never be over. From this moment forward, you need to concentrate on what is in front of you, not what has occurred. If your ex is turning them against, trust me, in time the children will figure it all out and they will then resent their father for what he has done to them. Kids are not nearly as ignorant as people believe. They will hear everything that is said from both your and their father, allow them the freedom AND SAFETY to make up their own minds. As for right at this moment, you need to take the time to focus on yourself. Make sure you are maintaining your therapy and anything else you need to do in regards to your bipolar disorder. Maybe you can't start working full time, but I am willing to bet that you could start working a little bit at a time and start feeling the reward of those pay checks, no matter how small they are, it is something you did all by yourself.
When you speak to the children, always try to remember to be upbeat and happy. Discuss their days and be fully present when they talk to you. If their father wants to be the guy that degrades you and others, let him have it. Just make sure you show your children that you do not have to resort to that behavior and rise above it.
Meditate a little bit each day, whether in prayer or in complete silence. Quieting our mind works wonders in helping us figure things out.
Thank you for the kind reply. You're absolutely right in all you said. It's been so hard I could hardly see straight. I'm a believer in our Father so prayer does help me much. Take care and keep up your comforting words to others.