mlsinokc.com looks like an adsense spam site/directory
your site looks like a real realty site...
It looks like two "different types" of sites based around the same subject.
I wouldn't be conserned with him suing you... and if he did, you've been online longer and look more like a real business then he does.
I'm not sure what you are wanting to do exactly... unless you have your domain name trademarked (and it looks like a city code and the code for realty, not something that would be trademarked) ... then there is really nothing I would be conserned about.
If you are worried that he is beating you in the serps, then you just need to work on your SEO and get back on top.
Oh, you could try to get listed in his directory as well.
Welcome to the community by the way...