Why is neither [I have met you] nor [I met you] grammatically correct?

I have made up the sentences below.

(1a) I've been very sad about failures after failures. I haven't talked to anyone until I've met you now.
(1b) I've been very sad about failures after failures. I haven't talked to anyone until I met you now.

(2a) I've been very sad about failures after failures. I haven't talked to anyone until I've met you at this party.
(2b) I've been very sad about failures after failures. I haven't talked to anyone until I met you at this party.

Most of my non-native English speaking friends think neither tense of "meet" is correct. They cannot explain why it is wrong. Please tell me why it is grammatically wrong. Thank you very much.

You have used the simple past and present perfect tense with "now" and "at the party". Why don't you use simple present tense "until I meet you"? for the present?

until I've met you now.
until I met you now.
until I've met you at this party.
until I met you at this party.

Perhaps:

I've been very sad about having so many setbacks. I haven't talked to anybody about it before I met you.

Also possible:

I never talked to anybody about it before I met you.

Are you practicing using "met"?

I'm not sure what you're working on, but none of those sentences work.

For a start, change ‘failures’ to the singular ‘failure’ every time, and the square brackets in the title to quotation marks.

All four of your sentences are wrong.

I think you probably just mean:

You're the first person I'm telling this to.
You're the first person I've told this to.
I haven't told anyone this before.
I haven't told anyone this until now.

You don't have to say anything about meeting anyone.