I wasn't paying attention to such things when I watched Gundam Wing, but I remember hearing that someone went through and discovered that everyone is too busy doing other things to be having sex. No two characters (or at least the Gundam pilots -- I don't remember if it holds true for everyone) have unaccounted for time at the same time and in the same place. Whenever two characters are in the same place at the same time, you know what they're doing the entire time they're together. Whenever any one character has time in which they could be sleeping with someone, everyone else is either busy or totally inaccessible.

So if this is true, you have to not care about the slash fitting into the plot continuity.