I Know It’s Usually Not Okay To Date Your Best Friend’s Ex But My Situation Is Different?

I’ve liked this guy since the 2nd day of school. He asked out one of my friends, so I was really sad… but I got over it and moved on. Well a week later, they broke up and he asked out my best friend two days later. Just so y’all know, she didn’t know that I liked him, so don’t go calling her a bad friend because she is awesome
So she said yes, and they were “dating” for like 3 weeks. The thing was, they didn’t do anything… like he never really payed attention to her and she didn’t pay much attention to him. They were never alone, and the only time they acted like they were going out was when they were texting… Yeah so it was almost nothing. I’m not even sure they even liked each other that much………
Without much surprise, she broke up with him, via a text message. Her text says “hey I think we need to break up it’s just not working” and his reply: “ok”. She wasn’t sad… at all. She actually said she felt better after they were done. Now my best friend is in a really, really good relationship and she’s a million times happier with this guy than she was with him.
So now there’s me, who feels neglected cuz my best friend wants to hang out with her boyfriend like… 24/7. I’ve been hanging out with other people, including her ex. And… I like him. Being around him just makes me feel really happy. Crazy, I know… but the thing is, I don’t think she’d seem to mind if we went out. She even told me one time that he and I would be cute together… this was while they were still “together”.
So what should I do? If you were my best friend, would you be mad? She comes before he does, so I’m not gonna do anything crazy but… what do you think?