Has he lost interest?

My ex (we’ll call him A) and I are still talking because we still love each other and he lost his virginity to me after our breakup. I broke up with him (3 months ago) because I wasn’t mentally ready. Freshly after our break up, I insisted he should talk to a girl (we’ll call her B) that I thought he’d make a cute couple with but he said no because he only wanted me. Fast forward to now, we’re talking still but yesterday as my guy friend was teaching me new choreography outside of school, I saw him walking out with B leaving to the store & he didn’t even look towards me when they came back. I wasn’t looking either but I knew because my guy friend told me. Also, they know each other.

Now today, she came to see a guy’s drawing at our table & I noticed that A kept staring at her. After that, she told our teacher she was leaving and stood behind his desk to fix some papers. Again, I noticed him staring at her. Should I back off?