I'm going to text my ex's new girlfriend
Why are you going to text your ex's girlfriend?
I want to know how she's doing.
You should not contact your ex's girlfriend. Doing this will make you seem spiteful and jealous. Instead you should focus on yourself and your goals.
We are not together anymore so I am going to text her.
Do you have something specific to say to her? If not, I am worried that you'll just be causing more drama than it's worth.