"solid, stable job appropriate for the kind of guy who is dating me"
It's certainly more difficult, but you could try to find a girl who wants you rather than 50% of your future earnings. You'll probably have a better time with her as well.
A little aside about being (and not being) salarymen:
My current landlord probably would never have rented my apartment to me if she had met me in my current state. However, when I first started living here, all I had to do was slide over my business card. The logo on it implies "This man will be no problem for you. He is of the finest character or he would never work here. If he is hospitalized, our CEO will walk his rent to your door and apologize for the inconvenience. Should you have any other issue with him, one call to us and he will wish he had been hospitalized. Guaranteed by the good name -- and virtually limitless capital reserves -- of $COMPANY."
Salarymen do not typically make a lot of money, but in a very status-conscious society, salarymen at particularly well-known companies didn't just draw a high card, we drew a straight flush. And we've got the next best thing to a signed promise from God Almighty that that status will never degrade in any material fashion.
I was once introduced to the mother of a young day I was seeing at the time. She was less than enthusiastic about me, mostly because of the one inalterable way in which I will never be ideal Japanese husband material. However, when I mentioned what I did for a living, you could practically see the gears turn in her head: "My grandchildren will go to only the best grade schools. They will always have enough money to pay for cram school. They will test into the best high schools, then universities, and then they will get jobs as salarymen just like their father and they will be set for life. Don't let him get away!" (She actually may have said that last bit out loud.)
I have a lot of sympathy for your point regarding materialism, but I have never begrudged the lady in question that thought process.
So anyhow: I have all manner of practical ideas on how to market a startup like it is really a soulless Japanese megacorp.
I hate to be harsh but I'm inclined to think the type of guy who wouldn't follow his dream because his girlfriend told him not to is not the type of guy who will be able to weather the amount of rejection and emotional stress that goes along with starting a business.
Perhaps it's not so much about "told him not to" than the fact that in many places, going off and doing your own thing is not normal, so it's pretty much guaranteed to be a point of contention, if not outright conflict.
I don't think Italy is nearly as bad as Japan from this point of view (I don't know Japan at all, though), but there's certainly more of a mentality among many people that it's for the best if you get a Permanent Job with a Stable Company.
It's certainly more difficult, but you could try to find a girl who wants you rather than 50% of your future earnings. You'll probably have a better time with her as well.