Hey guys,
I recently met this girl who has a 2 year relationship, but sometimes she "flirts" with me. I'm seeing a girl now and she's telling me, on an ironic tone, how she is very sad. She offered me to go to the shop for me in my exams.
A week ago we had this chat
She : where's your girl
Me : waiting for me at my house with a bunch of roses I guess

hah
she : But now I'm here you're not planning to go there do you

Me froze*
Okay, I totally froze after that comment and didn't know what to say. Any suggestions? I have a lot of problems how to handle freezes ( like you cannot say a word ) in general.
My second question is : we go for a drink a lot together, watch some movies. If she were single I would have already highered up my game, but she's not and I have fear to go for kino escalation.
Anybody can help me how to gradually build this up with this girl?
Thanks