There's nothing wrong with being a "fair weather" diver. I did my time on cattle boats in rough weather, carried my gear through the woods to the springs in full wetsuit in 95 degree weather, did the deep diving specialty, did my Rescue cert, etc...
Guess I've gone soft - but now I dive for enjoyment - not challenge!! You dive the dives you feel physically, mentally and emotionally "up" for. It's not a bad idea to take on a challenge every now and then - for the experience, but don't push yourself into doing a dive just because you feel you "should".
I agree that your hubby sounds obsessed rather than focused. I generally think of focus as being associated with attaining goals. So, your encouraging him to get advanced dive training is a good idea. That turns obsession into focus, shows that you support his love of diving, and something productive comes at the end of it - advanced certification, and the opportunity to train new divers. (sounds like he was a pretty good teacher for you...) Also, persuing advanced certs will put him in contact with lots of other divers in a more structured, rather than "social" situation - which may help him overcome his shyness, and find alternative buddies.
My husband and I met diving, and before we got married did several dive trips together. Living in Florida, I thought we'd do a LOT of diving after we got married - but he's also into golf - and diving took a back seat to that for the first few years (I started golfing too - but I'm not a nut for it like he is). I also went back to school for an advanced degree (life gets in the way of life sometimes). After I graduated, we started doing live-aboard dive trips in the May time frame the past couple of years, and that usually sets us up for a lot of diving activity over the summer and into the fall. (too hot to play golf for me!) The rest of the year is golf. I'd like to continue advancing my certs, too. But I also enjoy doing other things like playing golf - or biking - and even going to school. Turns out to be a nice balance.
Over time, you guys will find a way to work it out - you haven't been married very long. Relax. Give it time.