Dear god why- how do I fix this?

[Arkaeth]

I'm not missing any of the episodes, or CSS, or anything like that. I only started to have this problem recently, for no real apparent reason. I now have error signs for things that I once saw fine, and there are lots of floors that I see like this.

[psycho]

1. wipe the jizz off your screen


but in all seriousness, verify game cache files of things like HL2, ep:1, ep:2, maybe CS:S, and any other games including garry's mod.

also that dvl spelled missus wrong

[Nicknero]

1. wipe the jizz off your screen


but in all seriousness, verify game cache files of things like HL2, ep:1, ep:2, maybe CS:S, and any other games including garry's mod.

also that dvl spelled missus wrong

You as well. It is either Miss, or Mistress.

Anyways, don't get off topic here.
What it looks like is that you are a few corrupted content files, so the best thing to do is verify game cache and defragment your game files while you're at it. That will make your game go faster, and probably fix the weird textures/models.