Using "since" in past and future perfect tense

Question

As we usually say in present tense:

It has been twenty days since I met you last.

In past tense:

It had been twenty days since I met / had met you last.

Which tense should be used in the subordinate clause?

Now in future tense:

It will have been twenty days since I meet / met you last.

The present is okay but please explain the past and the future.

Thanks in advance.

Answer 1

The correct word is "met" in relation to your question.

"It will have been twenty days since I met her." "It will have been twenty days since I met you."

It is also worth adding a few other points.

1. The "last" would normally be in the middle of the sentence, not at the end.
2. When referring to meeting you, as opposed to meeting a third party, it would usually be better to use "we.

The following examples illustrate two points above.

"It has been twenty days since I met you last."

The above sounds clunky.

"It will have been twenty days since I last met you."

The above option is good.

"It will have been twenty days since we last met."

This third option is better.

"It will have been twenty days since we met [to discuss the proposal]."

This fourth option is also good.

Finally, in relation to future events, "meet" is correct.

"It will be twenty days until I meet her again.

" Or ..

"It will be twenty days until we meet again."