。
I stopped trying to keep up with fashion.
Literal
Trend [to-に] follow going [nominalizer-こと] [topic-は] quit.
ついていく (to keep up with / follow along) is often written in hiragana for the auxiliary 行く, since 行く here is delexicalized from its 'go' meaning. ~のはやめた frames the decision: 'I quit doing X.' A frank admission of stepping off the trend treadmill.