Between you and me
A common mistake in spoken English is to say ‘between you and I,’ as in this sentence:
X Just between you and I, I don't think it's going to happen.
In standard English, it’s grammatically correct to say ‘between you and me’ and incorrect to say ‘between you and I.’ The reason for this is that a preposition such as between should be followed by an objective pronoun (such as me, him, her, and us) rather than a subjective pronoun (such as I, he, she, and we). Saying ‘between you and I’ is grammatically equivalent to saying ‘between him and she,’ or ‘between we,’ which are both clearly wrong.
People make this mistake because they know it’s not correct to say, for example, ‘John and me went to the store.’ They know that the correct sentence would be ‘John and I went to the store.’ But they then mistakenly assume that the words ‘and me’ should be replaced by ‘and I’ in all cases.
Remember: the correct expression is ‘between you and me’:
√ Just between you and me, I don't think it's going to happen.