Seeing as a cousin isn’t a sibling, I think the laws of yichud apply here; but, I honestly can’t believe that anyone here considers talking to your cousin is a big deal, especially if you’ve been close to them since birth! The concern (practically speaking, not halachically) should be if that cousin is like a stranger to you, and not if she’s close to you (studies in kibbutzim show this to be the case).
It just seems so bizarre to me. This is anecdotal, but I’d never felt sexual attraction to any of my female cousins.