you’ll get through this

Three weeks into quarantine and my bf of three years tells me he changed his mind and doesn't want to build a life with me. We have been through so much together before this: both of our parents divorces, family medical issues on both sides, mental health breakdowns on both sides. We now live together and he just dropped this on me last night and is just going about his day today, like a weight is off his shoulders. I feel like I can't breathe. I don't know how to act or what to say. I'm falling apart on the inside and can't get out.