Had lunch with my ex girlfriend?

Yesterday, my ex gf of 3 months, who I've had very little contact with, came out of nowhere and sat down with me at the table I was eating lunch at. We were having great conversations, and I was making her laugh hysterically like old times. I have still had strong feelings for this girl, and it seemed like a spark was still very strong between us. So I decided to call her up today to see if she wanted to grab lunch together again. She said "sure," but I could tell the moment she said that that this could be a mistake on my part. It didn't sound like an enthusiastic "sure." Anyways, we meet up, and she's with 4 of her friends, 2 of whom I've never even met before. Hence, I set myself up for an extremely awkward situation. I sat down, and they were talking about stuff that I didn't know or care about, and thus had nothing to say. Meanwhile, my ex has barely even glanced at me, and has only said "hey, you can sit there." 10 minutes p, I scarf down my sandwich, and......................