My partner left before the start of last year. What tax froms do I need to file? Am I now a sole prop? I always filed a 1065 and received a K-1. How does it work now?

 You didn't mention whether or not you were formed as an LLC. If you were not formed as an LLC and operated strictly as a partnership, you would now be considered a sole proprietor.  If you were formed as an LLC and did not file Form 8832 to be classified as a corporation, you would be a single member LLC which the IRS classifies as a disregarded entity. 

In either case, you will report your business income on Schedule C which is available in TurboTax Self Employed.  You will NOT need to file a K-1 or 1065.  

If you did file Form 8832 to be classified as a corporation, you would then need to file the appropriate corporate forms.