Looking on the internet deeply has found these results:

It's been a long time since we met is the most popular phrase on the web.

It's been so long we met 16 results on the web	It's been a long time since we met 1155,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Perhaps I should ask for an introduction, as it's so long since we met. It's okay, it's normal, long ago since we met. But we met long before that. Alex, it's been so long we thought you'd gone into witness protection. It's been so long we thought we'd drop by and say hello. It's been a long time since we met one of us that actually wanted to hang out with. They were together long before we met and long after. It's been so long since we met.	It's been a long time since I've met someone with a chauffeur. It's been a long time since we all met as kids. It's been a long time since we've met a couple where we like both the husband and the wife. Welcome to my house, my dear Baron. It's been a long time since we've met. It's been a long time since we met one of us that actually wanted to hang out with. It's been a long time since we last met. It has really been a long time since I met him... Today. Even though it's been a long time since we last met here in Italy and we miss you, we always follow and support you.

It's been so long we met

16 results on the web

It's been a long time since we met

1155,000 results on the web

More popular!

Perhaps I should ask for an introduction, as it's so long since we met.
It's okay, it's normal, long ago since we met.
But we met long before that.
Alex, it's been so long we thought you'd gone into witness protection.
It's been so long we thought we'd drop by and say hello.
It's been a long time since we met one of us that actually wanted to hang out with.
They were together long before we met and long after.
It's been so long since we met.

It's been a long time since I've met someone with a chauffeur.
It's been a long time since we all met as kids.
It's been a long time since we've met a couple where we like both the husband and the wife.
Welcome to my house, my dear Baron. It's been a long time since we've met.
It's been a long time since we met one of us that actually wanted to hang out with.
It's been a long time since we last met.
It has really been a long time since I met him... Today.
Even though it's been a long time since we last met here in Italy and we miss you, we always follow and support you.