Please continue to cut Gareth a lot of slack. Fatigue can look and feel like laziness, but you know for sure it's not when you're missing out on fun things that you were really looking forward to, for lack of endurance.
It's a very real issue with scleroderma, and other chronic illnesses, that fatigue can make it simply impossible to do all the things we would normally do. It often exerts a shock on all aspects of our life: work, hobbies, and socializing.
When I realized this, I eventually rearranged my whole life to accommodate my varying and diminished energy levels. Now all my close associates know that there is an inherent "IF" in all the plans I make. I will prioritize whatever we have planned on, and I will do my best to pace myself and rest to try to be in shape for it; and i will look at other alternatives, too, such as maybe suggesting take-out at my place rather than dinner out, etc., whenever that's possible.
I've learned to never agree to do anything I don't really want or could reasonably plan to do, because with fatigue and illness, those things are the very first to bite the dust, so it is kinder to just firmly but gracefully decline the invitation, right up front. And to let others know, as soon as I do, that plans are going to have to be changed.
For what's left, I try to schedule and pace myself. I also expect to bite off more than I can chew occasionally -- because it's very challenging to predict the largely unpredictable -- and I try not to be too hard on myself when I pay the piper (because self-denigration and remorse also defrays that precious vital energy).
I strongly recommend simplifying life to the absolute max. Sometimes that simplification includes focusing our social life entirely around people who are flexible and understanding.
As Amanda so aptly and cogently pointed out, it is very stressful for us to try to maintain contact with people who are prone to being inflexible or not understanding. And it is pointless for anyone with low energy reserves to try to tolerate poor behavior or impaired relationships, simply because we just plain don't have the extra energy to invest in trying to sort those relationships out.
The unending stress of chronic illness will eventually cause us to either bend or break. I personally prefer bending rather than breaking, so I try to keep my goal as being flexible and resilient, instead of trying to plow along without realistic adaptations to the changing circumstances that less-than-exuberant-health imposes.
I know it's probably really hard for you to figure out what end is up with Gareth. But there is a handy rule of thumb to try to figure out if we are depressed or fatigued at the moment. Depression makes us just not want to do things, even fun things. But with fatigue, we really want to do things, but we just can't muster the energy to do them (or to do as much of the activity as we'd like.) Since depression can cause fatigue (and vice versa), it's helpful to figure out what's missing, the desire or the energy. Depression can zap both at the same time, but fatigue will only zap the energy, and not the desire.
Because fatigue leaves us still straddled with the desire but often not the ability, I've found it is most helpful to be frank and accept the situation as soon as possible, so that my own rebellion or guilt or disappointment doesn't drain my batteries even further.
Give Gareth some extra hugs, just from me!