Having a hard time

My boyfriend of two years is finally coming to understand and actively help me with my depression/anxiety. However he texted his ex behind my back and told her he missed her as a friend and missed how it felt in the old days before everything happened between them. Of course I found out from the ex which hurt 100% more, and damn me look stupid. She made it seem like she was trying to be on my side but then when I went thru the whole conversation on his phone she left parts out and even told him that she “wouldn’t tell Claire about the other text”. He apologized and said that he just wanted closure with her. I’ve still very upset it’s been two days. I’m not sure how to handle this and I would love some advice.