Ann Arbor is actually a pretty decent place to be for non-undergrads. You'll find that there are plenty of young professionals around (Ann Arbor is the home of a major Google office as well as JSTOR, and a number of firms and startups either affiliated with the University or the U of M hospital.) In terms of night life, there's good news and bad - the good news is that if you stay away from South University, you can avoid the largest concentration of party party party undergrads. The bad news, though, is that its impossible to avoid them altogether - Ann Arbor's downtown is small enough that even "grown up" places - like, say, The Jolly Pumpkin (Belgian style gastropub) or the aforementioned Ashley's (Microbrew focused bar - they have like 50 taps and rotate through really obscure beers) will have at least a few undergrads hanging around. They're usually pretty well behaved.
As for food, just check Yelp - pretty much every major cuisine can be found in Ann Arbor (although if you want a good and authentic taco, you'll have to head over to the East side of Ann Arbor or Ypsilanti.) If you can scrape together the dough, get a sandwich at Zingerman's deli for sure, and Zingerman's Road House (on Jackson on the West side of town) has been getting some national press for their modern barbeque. Seriously, though, if your boyfriend likes holes in the wall, send him post haste to Ypsilanti (Ann Arbor's poorer, grittier, less annoying neighbor, 10 minutes down the road) You can get a burger at Sidetrack (one of GQ's best 25 burgers in the country,) a breakfast the size of a semi-truck at the Bomber, the best Thai food in Washtenaw County at Thai-Thai (do take out though, there's literally 3 tables,) crazy good Tacos at La Casita, etc.
The Arb got mentioned in terms of primo outdoor zone, but there's also the Matthei Botanical Gardens just outside of town, and I believe there are 2 or 3 dog parks (you can get an off-leash permit from the city too, if that's your thing.)