Is it bad that I like my ex's bff?

Me and my ex were never anything serious. All that happened was one thing led to another, we ended up kissing and had a thing going for some time. Eventually, she admitted that she used me to get over her crush and we immediately split. She has been in a relationship with someone very toxic for the better part of 3 years now. He for some reason picked up a fight with me that I ended up winning. After that, I didn't speak to my ex ever again (about 2 years).

Recently, my friends introduced me to a girl from their uni and we ended up going out with her a few more times after that. The last time we met up we were flirting we each other, but it didn't go anywhere. A friend noticed and told me the bad news. She's my ex's bff and my ex has shit-talked me to her.

She hasn't said anything bad about me behind my back and acts really warm towards me. I don't know if it's a good idea to pursue her.

Is it bad that I like my ex's bff?
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