This is Jeffery. I inherited him from a relative about a year ago, and he has been thriving in his sunny window ever since (the second pic was from his glory days...). Until recently. He started to wilt and a lot of leaves were turning brown, despite not changing anything with the way I watered him. I removed him from his pot to discover his roots were very overcrowded. I repotted him and trimmed his vines because they were all brown and shriveled. 

That was about three weeks ago. And while he doesn't look like he's dying anymore, he certainly doesn't look the picture of health. He did bounce back a little bit after the repotting, but his progress seemed to plateau after a couple days. How to I revive him? I'm still learning a lot about plants, and I would really like to be able to bring him back from this instead of sending him to the farm. Desperate for your suggestions!!

Some background information in case it's useful:

* I have about two inches of lava stones at the bottom of the pot to help with drainage. In addition, the pot has drainage holes that lead to the connected base.
* I've been watering him roughly once a week, waiting until the soil is dry before watering.
* He's in a south-facing window and gets indirect sunlight all day (unless it's rainy, like today).

How do I help this guy (Jeffery)?