The people on the envelope are the people invited. I'm planning a wedding and we are limited by seating at the reception. As a bride, I would rather someone call and ask, so I could check my RSVP list and give you the green light or the "I'm sorry but we're limited to seats at the reception." spiel. It's not up to you who you bring, if you haven't seen these people in over a year, you don't know their financial situation as to why they only invited you and not "and guest" on the envelope and likewise, they probably didn't know you had a significant other. It's a really touchy subject, but, please, don't just show up with someone, there may not be enough seats to go around and that could be very uncomfortable for you/your date and the family hosting the reception. Err on the side of caution and call and ask the bride before anything else. It's not an attack on your friendship to not invite your other half, it's probably a budget/space issue.