It is rarely unethical towards the employer to leave employment, especially if you follow the arranged procedures for doing so in your contract.
In a reverse situation, your employer would not consider timing of your personal projects (such as having a loan/mortgage, or starting a family) when making changes such as redundancies.
However, before you quit, you may wish to explore other choices in-between "put up with too much work" and "quit". Neither of them seem pleasant.
I suggest talk to your supervisor and explain that you find the current workload too high. You need to do this in a reasonable, matter of fact way, quoting e.g. number of hours you needed to complete your assigned tasks in last week. No mention of quitting, or any outside influences that might be making things stressful - focus just on overlong days and total hours. Be prepared to talk through possible solutions that the supervisor suggests, they may not be things you had considered. Sometimes when you are stressed you may not be considering simple solutions - such as a company policy of time-in-lieu for overtime allowing you to take more time away after a long night than you currently do.
Your supervisor may also be expecting you to say "sorry, I think that will take me 2 days, I cannot complete it this evening" when assigning a task, or if it is not possible to predict easily then the next day say "sorry, I have not completed that task, I think I need much longer because..." - this is a matter of setting expectations. If you are a junior employee and the supervisor is also not experienced in judging how much work to delegate and how to track it, it could take a little while to settle on something that works for you both and is sustainable.
If your supervisor is reasonable, and has enough influence to help plan and fix things, then you may be able to find a middle ground. Even if this does not fully work for you, you will have made things less stressful whilst you consider your other options.
If your supervisor is unreasonable or behaves unprofessionally, or just makes vague promises about how things should get better, then you have another data point. Avoid reacting negatively to this, even if it seems unreasonable - but if you find the company being unhelpful or unpleasant to you after raising a reasonable concern, then you should have fewer moral qualms about leaving the project.
When quitting, it is better to search for alternative work whilst still employed. In that case you have an income, and will also be viewed as a more desirable candidate by employers.