I went to the garden (the park?) yesterday with my friend. I had a good time, we drank coffee and ate some sweets. She has my been friend from college for 3 years.

Yesterday, I went to the garden with my friend. I [we?] had a good time, drinking coffee and eating some sweets. She's been my friend for three years; we met at college.

If you want to make more complex sentences you could say this. Yesterday, I spent some time with a college friend I've known for 3 years. I had a good time as we drank coffee and ate some sweets in the garden. Hope this helps

Good Cedric but “... she has been my friend...” would be correct.