Welcome to the forums and thank you for reaching out. You're definitely in the right place. There are so many partners in the same boat as you so I highly encourage you to have a browse of the other threads and join in if you like. Here is the link to the other posts -
One of the top threads there is about supporting your depressed partner by Carmela which I'd recommend too.
To answer your questions, withdrawal is absolutely a 'symptom' of depression. When our moods drop, it's a very natural thing to withdraw from friends/family/society. Other signs definitely include being tired/fatigued and being irritable. Without knowing your husband, there's every possibility that the way he feels could be making him angry too - knowing that he's not feeling himself but not being able to fix it/make it better.
While Beyond Blue have a list of the signs and symptoms of depression, I really like this list from MensLine since it's a bit more specific to men.
As for the medication, GP's usually recommend 4-6 weeks to see any sort of improvement. Any side effects will usually taper down by then as well.
I don't think what you're wanting is unrealistic. It very much depends on the person as everyone is so unique in how they cope with depression. Sometimes people find that with help, they go back to their 'old normal', where as others have to create 'a new normal'.
I hope that this is helpful. Please feel free to ask as many questions as you like.