TLDR: I haven't been paid in a while and burnout is making me want to quit but the agency relies on me for a lot so idk what to do
I currently work as a project manager in a very small graphic design studio. I've been working there since graduating uni (it's been almost 3 years now) and I think I want to leave. I originally applied as a graphic design intern before I had to take on a social media marketing role since that's what the company needed until the beginning of this year where I'm now the project manager (however I'm still doing the social media stuff with a smaller number of clients).
We used to be a team of 3 until the lead designer left so it's just my boss and me. My boss also recently had a child so I'm keeping the company afloat (with my boss helping out remotely when he can).
The company relies on me for a lot. There are a lot of processes that I had to create (the social media thing) and things only I know and I possible can't leave now when the company is barely hanging on while my boss is busy.
My biggest frustration is I haven't been paid in almost 15 weeks. I've talked to my boss about on the start of July and he's explained that clients aren't paying invoices so he can't pay me. I was on a break last week hoping that I'd get something but then my boss explained he wasn't able to get to it during that week because he didn't have the headspace to follow up invoices because he's been busy and that he's working on it.
I take on quite a bit of freelance illustration work on the side and I've started feeling really burnt out and very 'no thoughts head empty' and just existing not living.
I’ve been in this agency for almost 3 years, I think I need a change. But is it ok for me to be selfish and do what will be best for my happiness? Or should I do what’s best for the agency?
And just to be clear my boss is very nice. He's very open about supporting a good work culture and facilitating good mentality and supporting me as a friend. It's just that recently I've started to feel that I know I'm not giving my best to the agency + the pay thing.