Due to differences in pronunciation and meaning, few native English speakers recognize that the verb behave is a compound of have. To behave is ‘to “have” yourself in a certain way,’ which is to say ‘to “hold” yourself in a certain way,’ which is to say ‘to comport yourself in a certain way.’ The failure to recognize the connection between behave and have is a sin of omission, but the widely held assumption that English have is a cognate of Spanish haber is a sin of commission: it’s a “sin” because there is no etymological connection between the two words, in spite of their similar appearance and meaning.
As proof, we remind ourselves of Indo-European sound correspondences. In particular, an initial h- in native English words corresponds to an initial c- (representing a k sound) in Latin words. For example, Latin cord- (and therefore the suffixed Spanish corazón) is the cognate of English heart, and English head is the cognate of Latin caput (which is why the capital is the “head” city of a state or country). Candidates for a Latin cognate of English have are limited to words beginning with c-, and the right one turns out to be Latin capere, which meant ‘to take, seize, grasp, grab hold of.’ While the semantics aren’t exact, the connection is that in order to have something we must literally or figuratively take hold of it.
So now the question is whether Latin capere left a Spanish descendant (which would therefore be the cognate of English have). That descendant turns out to be the verb caber, which has undergone a further change in meaning to ‘to fit.’ Something of that sense was already present in Latin capere, whose secondary meanings included ‘assume, adopt, contain, take in,’ and especially ‘to be large enough for.’