In my opinion, it is important not to expect an exclusive language partner, but to interact with different people in different ways.  If your expectation is that one person will teach you all you need to know for free, the odds are incredibly high that you will be disappointed.  

I do not think there should be a minimum commitment/requirement in order to use italki. I think it is important to talk about what your expectations are fairly early on with a potential language partner. I certainly wish more people would have done that with me, as it is possible that I have disappointed some.   I think it is especially important if you are a speaker of a language that is not in high demand and your partner is a native English speaker. I work on learning Spanish many hours per week, so in one sense I am a very serious learner.  On the other hand, I am just learning the language for the pleasure of learning it.  If it becomes not a pleasure to talk with a particular person, I have too many other teachers or partners available and will often start making different plans.   I think if I made a commitment for a certain period of time that would be a different matter, but I think when you get something for free, your expectations should be low about how long that will last.  It will only last as long as it meets the needs of both people. 

We can not require others too much. What we can do is to find the right person.