My ex texted me a few nights ago. Should I text her again?

Ex broke up with me about 1 month and a half ago. Tried to get her to stay. We hung out for 2 weeks after. She left for a 3 week trip. 2 weeks in I texted her to see how it was going. She asked me not to text her.

3 weeks after that I get a text around 9pm.

Her: I watched one of those episodes of Black Mirror we watched together and was thinking of you. I really hope you’re doing well.
Me: (about an hour later) Which one? And thank you. I hope you are doing good as well.
Her: The sad one with the dating app story
Me: Oh yeah. I really liked that one.
Her: Yeah, I actually watched it this time. ( a reference to how we would never finish shows because we would end up making out or having sex)
Me: (didn’t reply, 15 mins passed)
Her: Well, have a good night.
Me: You too

I felt like I was a bit too cold, but my brother was telling me to barely reply and keep it short. And he was right that she would text me. But I feel like I missed a chance to get a convo going and flirt. I want to text her back but he has said not too. To wait for her to text again. That was 2 days ago. I want to text her and maybe share that I watched the episode again and what made her think of me. He is adamant I will ruin my chances if I do. But he had a habit or holding grudges and I feel like I need to encourage her to keep texting me.

What should i do?

I want her back so don’t tell me to just let it go, unless that is to get her back. She is the love of my life.
My ex texted me a few nights ago. Should I text her again?
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