ex. Ex gf texting xoxoxo ... am I overreacting?

K.... so my fiancé is friends with an ex from before me (really short relationship) which is fine with me, but last night I glanced at his phone and saw it was her texting and it was "xoxoxo" right away I jumped on it asking why is she texting you that? He said he helped her find a car that the seller was willing to do payments. Makes sense as I knew he was scrolling kijiji and emailing on her behalf helping her out. I'm fine with them being friends but my panties got in a tight knot about the whole xoxoxo as in my opinion I am supposed to be the ONLY one sending those messages to MY man and her doing this is unacceptable and inappropriate! I told him that, and it will be on the table for discussion tonight. He ignored the text, but later was still chatting cars etc later that evening. I was shaking I was so mad but trying not to overreact. Thoughts?! (I do not know this girl personally but she just rubs me the wrong way). He thinks I don't trust him and am overreacting. 😢