I'm struggling to picture your situation - is it not an option for you to spend some evenings with your boyfriend and some with your university pals? Or do you feel compelled to socialise with both groups every night of the week? If so, perhaps this is where you're going wrong. Without wishing to sound like a kill-joy, I must warn you that you won't be going out every night of the week once you start work - you won't have the energy, most likely there'll be too much ground to cover to get to your desired destination, and you probably won't be able to afford it.
One unique and wonderful aspect of student life is that it lends itself to slipping out night after night (drinks are subsidised, the union bar is easy to reach, early lectures can be skipped - so why not?) but seven-days-a-week partying isn't quite a university REQUIREMENT. Social moderation might be an alien and vaguely tragic concept to you right now (and I'm not blaming you here - the prospect would leave me feeling aggrieved too if my student days were in full swing), but perhaps it's something you should consider, for the sake of establishing a balance between the two sides of your life. So how about it: an evening out with your friends followed by another out with your boyfriend? Is this something you might contemplate? If not - if the sacrifice required is simply too enormous - then maybe you should simply take a chance, swallow your anxiety and drag your boyfriend along to one of your uni soirees. How wrong could things possibly go? A bit of awkwardness, an instant of shyness, a moment of adjustment and surely your boyfriend would relax and get into the swing of things.
Or is there a risk that your friends' 'immaturity' might frighten him off you for good? If so, can you really be bothered to stick around with such a delicate butterfly?
Bear in mind that the friends one makes at university often remain one's best mates throughout life. So can you see your current social conundrum improving when your mates are pushing 30 and your fella is 42? If not, ask yourself if you really want to spend the rest of your days (assuming the relationship with this man lasts) stage-managing your social life so your lover and friends are never forced to breathe the same air.
But my guess is that your guy will manage just fine among your friends. Sometimes a bloke needs to be dropped into a situation where he's simply forced to survive. Honestly now - do you think he'll lose any sleep when it's time for you to meet his group of crusty thirty-something friends? I doubt it! He'll simply assume you'll cope. I think you should do the same.