Gather as much information as you and he can regarding MS and understand the ups and downs and all the issues that come with this MonSter.
Was he given a category of his MS? Is it Relapsing Remitting, Primary Progressive, Secondary Progressive.
When you say he is getting worse. What issues is he having and for how long?
Join a support group for MS patients and their caregivers. Attend MS informative meetings that are generally provided by one of the MS drug companies.
Google National MS Society for additional information. There are free mags that you / he can subscribe to: MS Focus, Motivator...
The absolute best tip that I can: Be supportive and try to understand.
Let's say right now he is getting worse and his legs will not support him and by tomorrow afternoon he is able to walk with no assistance. This is what this disease is capable of....MS: Unpredictable Disease of the Central Nervous System.