Mental health and pregnancy

Hey all, I'm curious about mental health and genetics. My SO (m/27) has a father with bipolar and psychosis, and he's worried if we have children that it'd be passed down. I'm 28 and want kids but he's paranoid about passing that mental health down. How likely is it that it would be passed down? He shows no symptoms of bipolar and I feel like he'd have started showing symptoms of it being passed to him. I'd just like some insight from anyone who may have had similar parents growing up and if it passed down to you or your children. Hope that makes sense, any help would be appreciated!