Having a girlfriend is not a lot to go on. What are you (and your SO's) interests? Do you want to establish a shared circle of social connections, or separate ones that occasionally overlap?

Dover expat here. It's getting better but if you want a walkable nightlife that's decent you'd have to live directly downtown, and it tends to skew younger due to it being close to UNH in Durham. Portsmouth is probably a better bet, but Dover is making gains on that claim. Just not so much yet.