、！、。
Oh, right! I used a condom I had almost never — or rather, I'd hardly ever — used.
Literal
Ah, yeah-yeah! Rarely [or rather-っていうか], almost used-[experience-ことがない] condom [object-を] used.
Casual blog register with a mid-sentence self-correction. っていうか 'or rather, I mean' is an extremely common conversational repair-marker, tightening a too-strong claim (滅多に 'rarely') into a more accurate one (ほとんど 'almost never'). 使用したことがない 'have never used' is the negative experience construction — the whole clause modifies コンドーム as a relative clause. The contrast between the polite ~ました ending and the casual self-correction gives a blog-diary feel.