I am a 50/50 owner in a small dissolving LLC. To this partnership I brought my software and through the course of several years continued to develop it. In the partnership agreement there is nothing on the ownership of my art/work/software. Who is the legal owner of this software/copyright holder?
Did you license your software or did you transfer ownership?
If you transferred ownership, then the LLC owns it and you have to figure that out.
If you licensed it, then the LLC would own that license and not the software.
If you didn't document any of this, things get quite a bit muddier.. did you work on the software during the LLC's working time and/or with its equipment? That generally makes the case that the company would own it.
Did you license it to other customers? Then it may help your licensing argument.
Did the LLC license it to other customers? The most common ways to do this are a reseller's agreement or that they own the software. The first might help you, the second, not to much.
If you want to take this software forward, I would recommend spending a bit of time with an attorney to get this figured out ASAP. If you're a student, quite often universities will have some free/cheap legal services you could use. If you're in the US, check out the Small Business Administration for their SCORE program - http://www.sba.gov/content/score
No one can give you a clear answer given the uncertainties and lack of important details. Down the road, one could likely make legal arguments either way for ownership of the software.
If you have a good relationship with your partner, the best solution is to put it down in writing that you own the software developed during the course of the partnership. To make it seem fairer, you could give him other things, such as rights to any trademarks. Or if you only need some of the code, you could ask for the code you really want and give him other portions of the code. Or if you want all of the code, you could pay some money to him. Try to be creative in coming up with a split of partnership assets that works for both of you.