the rot timer is calculated based on when the item is picked up using real world time. if you reload a previous save then most likely all of your things are now rotten
That, honestly, kept me from enjoying Fallout 3 after being introduced to the series via FO4. I understand that far in the future everything is going to be shitty and broken, but the raiders that just jumped me didn't seem to have any problem getting hits with their useless broken pipe weapons that I can somehow use to repair 5% of the durability of my shitty pipe weapon.
Fallout 3 is a shit game (The classic example of why is that things like stealing a spoon will get you sentenced to death by mob violence) Play Fallout New Vegas, it's built on Fallout 3's engine but instead of being designed and written by indentured interns at Bethesda it was made by people who are, you know, game designers. (I would kill for a NV-esque sequel to F04)
I'm currently making my way through FO3 and I haven't even discovered half of all the POI and I've been playing for months. NV piques my interest, because the story telling in FO3 is great, weapon durability aside.
Give NV a try. I don't think there's any reason to make sure to finish FO3 first (spoiler-wise), and you might end up liking it more.
They're both decent, but pretty long, so playing both back to back would be way too much Bethesda-jank for most people (though NV is def better, it is the same engine).
If I had to choose one, it would be NV every time.
Ooh! And if you have anything less than 100% durable then the game has a little flashing icon warning you it's not 100%. Couple that with the repair cost being the same regardless of the percentage missing!