Please Help....

I'm 23 weeks pregnant and I feel so much sadness in my heart. It has affected the way I sleep, eat, and do pretty much anything. My husband and I got separated since before I got pregnant. We've tried to work it out but he keeps running back to this girl. The girl keeps crying back to him so he leaves. I'm so tired of this situation. We already have a child and doesn't have a clue we are not together anymore. I've tired to stay positive for months but I just can't take it anymore.

How can I stay positive through this? I want to enjoy my pregnancy but it's so hard. I don't want to feel this way. Please help... any advise is welcomed.