How does it translate noun + ni + shiteitanda?

Question

I was trying to understand this sentence

kimi no senaka o boku wa tayori ni shiteitanda

kimi no senaka = your back boku = I

And I can't figure out what tayori ni shiteitanda means

jisho.org says tayori is a noun, dependence

and that shiteitanda is somehow related to suru jisho.org , if it's a verbal tense of suru I can't find it in the japanese verb conjugator japanese verb conjugator

Also, this webpage says noun + ni suru (in the case shiteitanda is related to suru) can be used to "decide on" a noun, ie "I'll go with.." . So may be this could be something of the form "noun + ni shiteitanda" assuming shiteitanda is related to suru, and since there is a "noun + ni suru" form but that's as far as I can guess. How does it translate noun + ni + shiteitanda?

Answer 1

"tayori ni suru" = to rely on

"shiteita" is the past progressive plain form of "suru"

"nda" is a contraction of "no da", which is used to present an explanation or point out something to the listener.

so in this case, we could interpret it as: "tayori ni shiteitanda" means the speaker ("boku") is pointing out that they relied on the listener's back ("kimi no senaka").