<human>: I [30] M, am in a relationship with a [31] F for about 18 months. We both have children and are divorced. Today we had our first parent meeting for her oldest daughter's cheer team.

I was there with my girlfriend and her two daughters. Her ex husband was there with his wife. The meeting ended and the girls wanted to show me where they were going to be practicing so I went on the floor. Their dad came out and was watching as well with his wife. My girlfriend was in the observation room talking. As she comes out, her ex walks over to us so that he can talk to my girlfriend. I move a little more away so they can have a conversation. (Side note, he has stated that he will not provide financial support for the cheer of his daughter and will provide transportation as long as it doesn't interfere with church.) 

As I moved, I intended to go spend time with girls but their step mother was essentially taking over, so I stepped back to the conversation between my girlfriend and her ex husband. I gave an intrigued look and her response was, "he said this is intense but I told him this will be good for her." I acknowledged in agreement and that was it. We left. 

Here is where my anger set in. When we get in the car, my girlfriend proceeds to tell me that her ex said he would pay for the uniform. I then asked, "when did he say this?" Her response was, "when you walked up." I asked why she didn't tell me when I approached. Her response was, "I didn't know how to handle it". 

My anger comes from feeling like she was more concerned about not hurting his feelings or making him feel awkward then telling me all of the truth. After I confront her about this, she tells me that the real reason she didn't tell me was because she didn't know how I was going to respond to the new information of her ex paying for the uniform. (Him not paying was a big fight that occurred a few days prior to this.) Am I right for feeling angry and upset?

Could you distill the essence of the text into 1-3 sentences?
<bot>: I was told a partial truth by my girlfriend in front of her ex husband.  Should I be as upset as I am?