変化のない毎日の生活に飽きていた。

。

I was tired of the unchanging daily routine.

Literal

Change's not-having every-day's life [to-に] was-tired-of.

変化のない modifies 毎日の生活 as a relative clause: 'daily life that has no change.' 飽きる with に means 'to be tired of / fed up with.' The ~ていた puts this boredom in the past, suggesting the speaker has since moved on or the situation changed.