We have been/become/made friends for three months.

[xiaoen]

Hi,
Suppose that I have a friend whose name is Kevin. I want to introduce him to some other people.

Hello. This is Kevin. We have been/become/made friends for three months.
Hello. This is Kevin. We have been/become/made friends since three months ago.

I have some doubts on the brown and blue parts. I don't know how to say such a sentence.
By the blue part I want to say that it's about three months that we are friends. We didn't know each other 5 or 6 months a go.

 

[Rover_KE]

Only 'We have been friends for three months' and 'We became friends three months ago' are natural.

 

[emsr2d2]

You could say "We have become friends over the last three months".

 

[krisfromgermany]

(not a teacher)
How about "We made friendship three months ago"? Is that correct, too?

 

[tedmc]

(not a teacher)
How about "We made friendship three months ago"? Is that correct, too?

You make friend with someone but you don't make friendship.

Our friendship lasted/has lasted three months.
We began our friendship three months ago.

 

[Rover_KE]

You make friends with someone but you don't make friendship.

Your other suggestions are not natural, tedmc.
Your other

 

[krisfromgermany]

(not a teacher)
Another suggestion, what do you think about it?

"We started/began being friends three months ago."