You have a few options:
You can contact them, offer to take them to lunch if they're local-ish, and see if there's any potential or willingness to collaborate. Maybe you each prefer to handle different aspects of the market.
Or, you can decide to not lose focus, and you can concentrate on the clients and customers and market that you have. Continue to do what you're good at doing, and keep slowly improving your product or service. So, maybe you won't be the biggest player in your market ... and maybe that's OK.
Or, you can learn to really enjoy competition. (I love it.) You can use this as a great opportunity to get free advice on areas you can improve, because all you have to do is keep an eye on what your competitor does. But, don't become defined by them. Try to figure out how to be better than them. That doesn't necessarily mean being cheaper, or shinier, or faster. That just means figuring out what your customers want, and then doing the best job of providing that that you can imagine. You have to be able to have fun competing with the other company. Being genuinely friendly with them (and helpful to them!) while trying to think up ways of putting them out of business, that sort of thing.
"Rules for Revolutionaries" is a great book that touches, in part, on handling competition. It's a quick read and fully worth it, if you have the time or inclination.