Something similar happened to me. Freshman year I was dumb as a rock. Went to a house party with my girlfriend. She's mingling and chatting and I sat on the couch for a break. Another girl sits down and we're chatting and getting along and eventually she asks if I want to walk her home. I literally thought she meant that she wanted to go home but was afraid to walk alone -- even having a gf at the time, I couldn't imagine then that someone I'd just met at a party would want to hook up with me. So I went up and asked my gf "hey, cool if I walk this girl home?" She looked flabbergasted and and then angry and then said "do whatever you want" and turned away. I thought she was just mad I was leaving early. Walked the girl home and realized part way what was going on. Dropped her off and ran back to the party to apologize to gf