depression.. family dilemma- should I stay or should go?

I have been through alot growing up. From a traumactic experience to depression. . I would like to say that I have done well so far, jus as long as nothing triggers it again. I am now a mother of 2 with one on the way. Unfortunately my partner of 7yrs suffers from depression and mental issues nearly all his life which still to this day affects his behavior and sense of judgement. He is a lovely man whom I love.. at the begining of our relationship there times when i couldn't cope with it all and tried to just leave him, but his suicidal tendancies and my love for him brings me back. I worked so hard to make it work and to be there for him while im going through a rough time myself.. I always believed that it was just a bump in the road and our love for each other will get us through this. And I did.. after a brief separation, to see where our feelings are at and what we want, we realised that life with one another and our two beautiful kids is what we truely want. It was so hard on us both to be apart and took its toll on us both. We finally came to a mutual respect and understanding for each others needs/wants/feelings/understanding and are more in love now than ever.. everything was perfect the way it should of been from the begining. He was getting the help he needs and on the road to a life together. We finally set a date for our wedding and planning a fresh new start with our kids and new baby on the way.. it was great until a few days ago when I received the most devastating news that had turned my world upside down. He cheated on me two years ago. Not only that, it was with a family member. In our own home. Im disgusted, ashamed most of all sick to the stomach because if who ot was with. All my dreams came crashing down. I dont knw what to do. One hand He's at a sensitive state at the moment, resently diagnose bipolar, severe depression was amonst it. He tells me im his everything, that life is not worth living without me.. its a bad call he made and regrets it more than i will ever know..he did that during a time when he was ay his most depressive state, alone and felt unloved, umsupoorted and unwanted by me. I was going through a time where all my energy is spent on our daughter the house, bills and just everyday pressure life was throwing at me also I was heavily pregnant with our second. I was in need of his support and took it all out out him when he's not there for me. I had no idea he was battling his own demons and needed me as well. It was a toxic year for us both. But we still got through it together. My daughter is such a family orientated girl, this would crush her. She picked up on my sadness and her father's sadness, and begged me not to send her daddy away again. This broke my heart even more. Shall I stay for my kids? My partner is now depressed more than ever at the thought of losing us. I even caught him browsing through through the internet for ideas of ways to commit suicide. He's only just starting to see a professional too. Im afraid this will make him give up on life. Despite/apart from the horrible deed he did, hes still a great father and person. But I don't know if I can ever get pass this betrayel.. im 50/50 on what is the right thing to do.. shall I keep my family happy and stay? I will be devastated either way. I was told that only I know what is right. . But thats something I don't want to hear because I have absolutely no idea.