Domain name question

I own a domain name for example 12*3.com

A buddy thinks the name is great and opens a corporation called (without asking me) 12*3.com

We start working together keeping whats mine seperate (domain) and whats his seperate (corp) but we both benifit mutually $$ working together.

Does the buddy have any legal right to my domain as his corp expands? Could I take the domain and idea and do/sell/etc whatever I please with it as I owned it 1 year prior to meeting the buddy?

We have not singed any agreements.

Thank you in advance

I don't practice in this area, but I think you have a partnership that would be governed by the default partnership laws in your state.  You brought the domain name and he brought the corp, but you've blended them at this point in the partnership.  Doesn't matter if you haven't signed any agreements, because state law has default agreements that likely govern this.

State law will govern what duties and rights you each have.