Hotels are great at keeping secrets. What happens in the room stays in the room. (And whatever it is, the maids have seen it before).
And regardless whether your "secret" already has a boyfriend or not, the best place to keep it is at Chandler Studios, the new tastefully discreet boutique hotel now open in the South End.
The first step to keeping a secret is covering your tracks, as in dropping your car (a rental, just to be safe) in a private assigned parking space before slipping into your room via keyless entry system without so much as fake smiling at a staff member.
Any of the 11 studio rooms should be sufficient for whatever covert ops you had in mind. Think brick walls for sound isolation, spacious bathrooms for freshening up, and vintage photos of the South End neighborhood. (No secret there, they just look great.)
Then again, if you're looking to keep a long-term secret a la Don Draper, you may want to reserve the luxurious suite for days, weeks, or make it the best month that you'll never speak about with anyone ever again.
And thanks to the 24-hour on-call staff, you'll never have to leave the room unless there's another "secret" you have to keep somewhere else.