<human>: Can you condense the text into three sentences or less?

So my boyfriend and I have been together two years. 

His mom revealed to me that her mother was bipolar and killed herself. She also told me that many others in her family had bipolar disorder/drug or alcohol abuse/many others.

She asked me to keep this a secret from my boyfriend, which puts me in a shitty spot. She says she'll tell him someday, but she doesn't feel he's ready yet. 

I think that this information is really valuable, it explains a lot of her parenting and makes me totally understand things I thought previously were strange/overprotective. My boyfriend has had horrible anxiety, and although he is much better than he used to be.... Maybe he would want to know that it runs in his family? 

What happens if he finds out I've been keeping this from him? What do I do? I don't want to break his mom's trust but I also DON'T keep secrets from my boyfriend.
<bot>: boyfriend's mother revealed his grandmother killed herself and he has a significant history of mental health issues. Do I keep her secret or tell him?