I remember this question popped up some time back, and it had no context then either. Well, in the absence of context, the simplest answer is that Sparta and Crete have been part of the same country since 1908. If that counts as a diplomatic relationship, then yes.

If it's international relations that you have in mind, then the only times when Crete has been a discrete, united, and independent state have been from 1898 to 1908, when Sparta was an insignificant town; and (probably) in the mid-Bronze Age, before ca. 1450 BCE, which is before Sparta existed. In either of those cases, the answer would be no.