If it gets out that I bought that uniform to make my ex-girlfriend do fake-schoolgirl roleplay...
Literal
That uniform, ex-girlfriend [to-に] 'fake' high-school-girl play make-do [as-させる] [in-order-to-ために] had-bought thing-[copula-なんて] if-exposed-[-たら]...
前カノ 'ex-girlfriend' is a casual abbreviation, shortened from 前の彼女. なんちゃって (the 'fake / just kidding / pretend' adverbial) attaches to a noun as a modifier, 'fake X,' used playfully or dismissively — 'pretend high school girl.' プレイ 'play / roleplay' is a loan with an adult-content register. させる (causative) + ために (purpose) stacks 'in order to make her do X.' The trailing バレたら '...if it were exposed' leaves the consequence unstated — a dramatic trailing clause.