Is she in a rebound/trying to create jealously?

I broke up with my ex because I had a lot going on in my life and I didn't think I was ready to pursue having kids and getting married so quickly. We dated for about 9-10 months in total. We broke up at the beginning of February and actually ended up hooking up on three separate occasions during the next month. The last time we talked was on Feb. 28th. She had left me a break-up letter explaining that she would always still love me and wrote several songs about us, saying "we could get back together" if I wanted too. At the time I didn't, I needed time to sort things out. Its now a month or so later and I just found out that she is dating a guy (past friend of mine) that I played sports with for awhile. I randomly texted her and told her that I was sorry for my behavior and that I wanted to see her one last time. She said she didn't want to meet up. She told me that she was truly happy now and that what she had said in the past is no longer relevant and I should respect that she is in a relationship now. This all happened very suddenly. What should I do at this point? Do you think this would be considered a rebound and she is just trying to make me jealous? or has she truly been able to move on so quickly? I know there are a lot of variables that play into this but I want to know what others think about the situation. Thanks.

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