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Human beings are pretty simple creatures are heart. We are formed by evolution to pair up and reproduce. The forming of romantic bonds is therefore central to our lives and central to our stories. And there are only so many choices for the people we can form romantic bonds with: friends, acquaintances, and strangers. 

So, yes, best friends of compatible inclinations fall in love. It happens a lot. You can put it in your story. It is not a cliche, it is life. 

How you tell it, on the other hand, may be a cliche. What makes a cliche a cliche is not that it is common, but that it is done in a lazy way. A cliche is a piece of writing that relies on the recognition of the common as an abstraction, rather than clothing it in the specificity that real life and story both demand. 

Because yes, best friends fall in love. But no two couples are exactly alike. No two love affairs are exactly the same. You can write a generic love affair, failing to give it any specific color or texture, or you can write a fully realized, full textured, fully specific love affair. They are both instances of the old familiar best friends falling in love pattern, but one will feel cliche and the other will not. 

Nothing that is fully realized, based on a mature and insightful vision, will ever feel cliched, even if it describes the most common pattern of human behaviour. It is the quality of the vision that matters, not the common nature of the events.