Where do i go?

My partner has chronic depression and anxiety. He'd have mental breakdown a few times every week. We've been together for 5 years on and off 3 times now. I love him so much and i try my best to always be there for him, giving him affirmations/reassurances everytime it happens. I can say he has been improving a lot for the last 5 years.

I'm initially a very positive person or at least i can regulate my emotions and feelings really well. But to be very honest it affects me quite a lot too. It is super tiring mentally for me to always have to be the extremely positive for him and it often feels like nothing works to get him back to his normal headspace. Being half-hearted won't do well for him too, he'd feel abandoned and ignored. So i always go all out tending to his mental breakdowns.

I feel useless, i feel helpless, but i can't ask him to support me mentally because he's also the reason i feel that way. I don't want to go to my best friend because i know she'd tell me to just let him go because I'd get pulled in even more while trying to pull him up. It's all paradox.

Now it's basically me left alone having these feelings all bottled up and pretty much have to handle it all on my own while i also handle his brittle mental state. Psychologist/psychiatrist is too expensive, it's not an option. I don't know where else to go and let out my feelings and thoughts to...