You mention this is a small company, and nothing in your description indicates you're in a death march in the sense of a project which is so large or unpredictable that no amount of extra resources will make it complete on time. But clearly there is a problem with expectations.
But at this point I've now worked probably 50-60 hours of overtime in the past couple months
60 hours' overtime over the course of two months - i.e. about 1.5 hours per working day - while this almost certainly means they're wearing you down and is certainly far beyond what you should even consider doing uncompensated is not in of itself indicative of a doomed project, especially if you're the only one doing it. How sustainable it is for you personally, of course depends as well on your base pay, normal hours, commute, other demands on your time, which we can't answer.
The company has always been small. We lost a guy 6 months ago to a new job, and I expected that we were going to hire a replacement for him, but this hasn't happened.
There are several possible explanations for this:
- The company is committed to hiring a replacement but genuinely cannot find anybody suitable.
- The company is committed in theory to hiring a replacement, but nobody personally has got around to kicking off the process or taken responsibility for keeping it moving.
- The company cannot afford to hire anyone, either because of cashflow issues or because the projected revenues will never pay for their salary.
If it's type 3, you definitely and urgently need to look for another job, because your job is not secure, and insofar as it is it will probably be demanding overtime regularly. If either of the other two are the problem, you should still be looking for other jobs as they're still red flags, but you should also be looking to solve the problem internally, as in this situation you might have some leverage.
- asked at what point overtime will no longer be required?
- asked what the timeframe is for replacement, and who is overseeing that process?
- requested vacation?
- requested time off in lieu as a condition of overtime?
- requested a level of overtime pay which would make you be willing to work 9 hours overtime a week?
- indicated a desire not to work overtime constantly?
If not, or if you've not had a clear answer, have a conversation with your manager about whichever of these things is most important to you and/or is most relevant to the business. You're unlikely to get remuneration for overtime in the past through negotiation and it may be unwise to try (especially if you agreed to work it unconditionally, employers don't like surprises), but you should be able to establish some ground rules for when overtime is agreed in the future. Your conversation might start with something like:
I wanted to talk to you about the hours we're working. I totally understand that sometimes overtime happens and is needed. As you know I've been working 7-10 hours on top of my working week, but that's not sustainable in the long term, so I'd like to talk about how we manage that in a way that works for everyone.
... and how it continues will depend on whether your preference is for less overtime or more money.
Your goal in that conversation will be to pin your manager down to specific timescales. If they won't commit to specifics, good intentions are worth zero, and you should weigh incoming job offers against your current job as it stands today, overtime, workload, holiday and all.
Remember, they're asking you to work overtime. It's up them to make a compelling offer and up to you to decide if the offer is good enough for you to agree or to refuse. So long as you keep agreeing, it won't be a priority to either hire or find some other way of reducing your workload.
Don't be timid in negotiating overtime. The point of overtime arrangements is that the business acknowledges a cost to overtime and is therefore incentivised to avoid it except where it's truly justified and does not simply heap that cost on you.