So I never thought about it before, but you are so right! There really is no indication that Remus is actually happy about his relationship with Tonks. The closest you get to that is when Teddy is born... but I think I' going to have to reread that part now, just to be sure...
I never really paid attention, because while I started as a Remus/Sirius shipper (mostly because it really is so very cannon ^_-) I moved quickly on to Snarry. I'll have to pay more attention to them when I reread the books again. ^_^