Mentally ill “boyfriend”

I love my boy (the reason I have quotation marks is because we don’t have labels on it again) we dated for 4 months last year and then he ended up breaking up with me because he couldn’t handle a relationship, as much as it completely ripped my heart out of my chest I accepted it although I cried for months straight, we still talked occasionally off and on throughout the next 5ish months that we weren’t together and I still found myself completely heartbroken over him, he actually came back into my life a couple months ago and I couldn’t have been happier, he is my person and I can’t move on or let him go, there was a couple days where he was super distant and I let him have his distance because I understand it’s hard for him, he ended up messaging me a couple days after and apologized for how he was being stand offish, he told me he’s not doing well and I knew that because of all the things he’s been through, I’ve been told to move on and that I “don’t need to love him” because he’s mentally ill and “drains me of my happiness” but when he’s at his highs I know he cares about me, I can’t just let go of him and leave him in a time of need, I would spend the rest of my life regretting my decisions, I just want to know what I can do to make him communicate more, I want him to tell me when he’s upset instead of being distant, I want to show him how much I care but I don’t know how to anymore, can someone help?