At the end of episode 15 (in Season 2, as defined here) titled El Sid, Sid's girlfriend slides again together with all the others, but then in the next episode she is no longer there.
Am I right or am I just watching the episodes in the wrong order? If I am right where did she go?
According to the link you provided, Fox aired the shows out of order.
Episode 15 El Sid should have been followed by Episode 14 The Good, The Bad and The Wealthy.
However, from the episode summaries (link), there is no mention of Sid and his girlfriend anywhere other than episode 15.
