It's virtually a certainty that he's paying you via 1099 reports.
In which case, taken together with your freedom of action: setting your own hours and time of appearances, etc., you're going to be deemed a sub-contractor.
The fact that he's also a C-10 contractor does not mean that you're not a sub.
If you only work side by side with him -- and he's calling all of the shots -- then the authorities ( especially the IRS ) will deem the relationship 'contractor with employee.'
That you both have left it fuzzy just means that the attorneys will have a field day making every issue a point of litigation.
Telling the Court that your relationship is 'up in the air' -- and that even you can't figure out whether you're an employee or a sub-contractor -- will have the judge pounding the gavel right on your head.
All Courts, at all times, hate, hate 'fuzzy.'
That's the primary reason why real estate deals have to be done in writing. Anything not written down in such deals is entirely disregarded. This provision is actually the reason we speak English.
[ The Angles were a Danish/Viking tribe that conquered hunks of Ireland and Britain. During their rule only land deals that were written in Anglish would be honored by their courts/ barrons. Stepwise, the underclass/locals started to use their master's language for all business purposes. The native tongue was never transcribed into a written form. Eventually, the British Isles became known by the rest of Europe as the place where Anglish was spoken. As pronounciation changed -- the land of the Angles became the land of the English. Then they were conquered yet again by the Normans ( Norsemen/ Vikings -- again ) this time launching their attack from northern France, 1066.]
So, if you've got a legal bone in your body: draw up a contract that spells out the terms of your deal. Reduce everything to writing, now, while there's no dispute underway. In his way, you can head off legal troubles when things turn ugly.
You should take the mental position that he's just a GC and you're a C-10 sub. Spell it out.
Or, you should take the mental position that you're just a part-time employee. Spell it out.
The Courts will not allow you to cross over and back. You'll not get away with being two-hatted while dealing with just one contractor.
And, naturally, everything at every turn will be interpreted in the worst light imaginable, by the Courts, since you've left everything 'fuzzy.'
In California, your number one threat is the State Tax Authority. ( Board of Equalization ) They are far, far worse than the IRS. Ask around.