Feel alone in relationship

I have been in an on and off relationship for many years now. My partner suffers with depression and suicidal thoughts. I try to be there for them but I have been hiding that I am struggling with my own mental issues. He sees me as a smiling sally and positive patty but I am just pretending because I don't want him to feel worse if I am sad. How can I show up for him, if I can barely show up for myself? When he gets depressed, I feel even more alone because I need him but I don't want to put that on him. Instead I try to distract myself so he doesn't notice anything wrong with me. Anyone else going through this???