He should definitely get in to see a doctor. Even if he was on the correct amount having to go see his dealer to get them would be a huge trigger for me. I too was a regular H user for years regularly doing $200 + a day (which on the low end would be at least 1600 mg of oxy) and I started out at 12 mg of suboxone a day and quickly went down to 8. For me I see no reason to be on more than that. I know a few people who are taking 32 mg a day for a norco habit which seems crazy.
It does take a few days to get used to the medication when you first start taking it. Sweating and dilated pupils are pretty common and can closely mimic full opiate side effects. If it continues he might be on too high a dose (Another reason to see a doctor). If you use right after you take the medication you will not feel much from it depending on your dose. Another reason why doctors prescribe higher doses is to keep you from getting high should you use. If you skip a day and use the high might not be quite as good, but you will definitely feel it. The only way to truly know if he is using is a drug test and I doubt you want to start playing those games.
I hope he is getting some other outside support (which I kind of doubt since he is scoring subs from his dealer). I struggled for 5 years to quit H and hadn't been at it as long as your boyfriend has. Meetings, outpatient, inpatient, one on one therapy or whatever it might be OR a combination of them. It is a very tough drug to kick and most users I know that have been at it several years have pretty low bottoms unfortunately. Your brain remembers how it feels and takes a good 6 months before you feel semi-stable and often longer than that.
I hope things work out for you. Take Care!!!