Unknown grammar

[asfalios]

Hello.!

友達でいたいと考えた。

What do you guys make of this でいたい structure?

I have never come across it before.

Many thanks in advance.

E.A.

[y suzu]

I'ｍ not sure if this is 100% correct, but I checked 広辞苑(こうじえん), the most famous Japanese-Japanese dictionary.
It says
で is a 助詞(じょしparticle)
1.1.6
事情・状態を表す。
（expresses the situation)
after で comes a verb or an adjective
友達でいる
いたい is "want to be"
so it means
lit. want to be being friends (with someone).
so, 友達でいたいと考えた。
ｍeans
thought that (I) want to be being friends.

I hope this is helpful for you.