Ezekiel 28:14 does the Hebrew say you were the cherub or placed with the cherub?
The Hebrew says "You [are/were]" but the spelling is unusual. In context we would expect a masculine form, but the word for "you" is in a form that is usually feminine (אַתְּ).
If we do not take into consideration the vowels (which were not written in ancient scrolls, but only preserved by oral tradition), the word looks like it could spell אֶת, which can mean "with." This appears to be the reading followed by the Septuagint.1
1 μετὰ τοῦ χερουβ ἔθηκά σε.... Alfred Rahlfs and Robert Hanhart, eds., Septuaginta: SESB Edition (Stuttgart: Deutsche Bibelgesellschaft, 2006), ΙΕΖΕΚΙΗΛ 28:14.