Actually, you could probably quit and it wouldn't be as big of a deal as you expect. Most people over-estimate the risk of quitting. And most people are a lot more understanding than we give them credit for.
Every time I've reached that point that you have described, I've quit. It was the best thing for me every time, too. There is no point wasting your time doing something you don't want to do, especially if it's for someone you care about. You'll just do a shitty job and you don't want to dump shitty jobs on people you care about.
Is it just that the work is boring, or are you being asked to do unethical things? I mean, either way, I would quit, but if it's anything unethical I would urge you to run as fast as possible.
However, if it's just "boring" work, perhaps recasting it in a different light might help. Look at it as a game of seeing how many you can finish in a single week. Stop worrying about doing the "best" job on it. If the project is so boring to you, then you probably shouldn't care so much about the quality of it. Just dump out some garbage, get the checkboxes filled, see how much you can get away with. Make it a learning experience, a chance to test your boundaries.
The other point is that if this is your BF's project, you are in serious danger of building up a load of resentment for him and breaking up the relationship if things get any worse. It may actually be better to tell him that you're not getting on with the project and it'd be better for your relationship if you work in different places. There's nothing wrong with that.
This job is not directly for the startup. I have been contracted out by the startup to this job and the money it brings is important for the startup atm.
That changes things a bit. If you believe strongly in the startup's strategic goals, then perhaps you can convince yourself that your current goal is purely tactical, and can indeed force yourself through it with willpower alone. Sometimes -- rarely, IMHO -- flogging yourself to get through some necessary shit work does make sense.
If you were actually working at the startup, on its principal mission, then your problem would be more complex. Not only would you have to think about the appropriateness/advisability of the particular feature you're implementing, but you'd have to constantly evaluate it in light of your relationship with your SO and your prospects in the new company. It would be very difficult to separate these questions in your mind, so IMHO it's a good thing you don't have to.
I think mnw21cam's point still stands - if working at your current position is "seriously affects the quality of [your] life", you need to prioritize that over making money for your boyfriend's startup, or you'll hold it against both him and the company for making you do something you don't want to.
Take care of yourself first, even if it means a slower launch for the startup! And it sounds like you have good coding practices and are well-regarded at your current position, so hopefully you could find another job that is more aligned with your values. Best of luck!
Every time I've reached that point that you have described, I've quit. It was the best thing for me every time, too. There is no point wasting your time doing something you don't want to do, especially if it's for someone you care about. You'll just do a shitty job and you don't want to dump shitty jobs on people you care about.
Is it just that the work is boring, or are you being asked to do unethical things? I mean, either way, I would quit, but if it's anything unethical I would urge you to run as fast as possible.
However, if it's just "boring" work, perhaps recasting it in a different light might help. Look at it as a game of seeing how many you can finish in a single week. Stop worrying about doing the "best" job on it. If the project is so boring to you, then you probably shouldn't care so much about the quality of it. Just dump out some garbage, get the checkboxes filled, see how much you can get away with. Make it a learning experience, a chance to test your boundaries.