South End has crazy amounts of good food. Around there specifically, I would recommend ilona (Mediterranean small plates), Barcelona Wine Bar (for paella), and the Beehive (more upscale bar with food and live music) but that's far from an exhaustive list.

Anywhere in the city is accessible with a T pass, which you should both get 7-day unlimited given you will be traveling on it a lot, so really don't just be confined to the South End. Hell you could walk from there to anywhere if you're committed enough.

On weekends there is plenty of a bar scene downtown for really all ages.

Other than the Freedom Trail, I would really recommend the Harvard Arboretum if the weather is nice, the MFA and Isabella Stuart Gardner art museums, and the Main Branch of the Boston Public Library (really just to look around at the beautiful building).

You're coming at a transition time where the weather could be great or horrible so really pack for whatever, but if you look around (including the threads in this subreddit), you'll find plenty of indoor and outdoor activities. Hopefully at least one day it'll be nice enough to just go out and explore at least one of these linear parks: the Emerald Necklace, the Commonwealth Avenue Mall and Boston Common, and the Charles River Esplanade.

Those are just my general ramblings, have fun! Don't be afraid to ask anyone for help, everyone here is really in their own heads and looks mean until you talk to them.