What happened first: "ye"/"you" merging to "you", or "thou"/"thee" falling out of common use?

Simple subject "I":

I went.

Replacing it with "me":

Me went.

That sounds strikingly wrong. We use it for fake "caveman talk".

However, there was a time when it worked like this:

1st person singular, subject/object:

"I"/"me"

2nd person plural (or polite, formal etc 2nd person singular, yes), subject/object:

"ye"/"you"

Speakers at that time would say:

Ye went.

and would find:

You went.

to sound wrong and weird in the same way we currently find:

Me went.

So what I'm wondering is, how did this "ye"/"you"-->"you" merger happen?

Was the "ye"/"you" form just much more rarely used at the time?

If so, I would expect the merger would have happened before the dropping of the "thou"/"thee" pronouns.

Is it known if this the case?

I would guess the question might be a little complicated by dialects developing differently in isolation, and then influencing each other later, but still, is there a general clear answer to:

Was "ye"/"you" merged before "thou"/"thee" was dropped?

In Old English, thou was used for addressing one person and ye for more than one, both as clause subject. Thee and you were used as object.

During the Middle English period, ye/you came to be used as a polite singular form alongside thou/thee.

During Early Modern English, the distinction between subject and object uses of ye and you gradually disappeared. Ye continued in use, but by the end of the 16th century it was restricted to archaic, religioous, or literary contexts. By 1700, the thou forms were also largely restricted in this way.

(Adapted from ‘The Cambridge Encyclopedia of the English Language’ by David Crystal.)