Remember: an oral agreement is worth the paper it is written on. The first question an attorney will ask you is, "What are the terms of your agreement?" Chances are that you and your landlord never even considered the possibility of subleasing, much less discussed it and came to a defined deci-sion. If that is the case, you are not in breach of any lease provision by subletting. Therefore the simple answer is that your landlord cannot evict you for subletting a desk.
But the question goes beyond that simple question and answer. Aks yourself and even simpler question, "Can the landlord get rid of me without reference to the sublease question?" The answer to this is, yes. He can give you a notice of termination, most likely a 30-day notice...unless of course the two of you discussed and agreed upon a different notice period in your oral agreement.
If you really want to stay on, if you do not have an oral agreement for a fixed term lease for less than one year, and if you can survive without your subtenant, work this out with your landlord.
First, read your commercial lease. Does it prohibit subleases? If so, your landlord will probably win.
Second, whatever your space sharing agreement says is not controlling, it appears that the individual is paying "for use of a portion of" your commercial "space."
Third, I agree with my colleague, you need to try to work it out with your landlord, otherwise you could end up in expensive litigation or forced out.