Found out my bf stayed with his ex after we became exclusive — don’t know how to process this

We’ve been dating for 7 months now. Around 1 month into our relationship — right after we agreed to be exclusive — my boyfriend told me he was going to Colorado (Boulder) for a week for academic reasons.

Recently, I found a birthday card to his ex tucked away in his drawer while I was looking for something else. Some of the things written in it felt emotionally intimate and didn’t line up with what he had told me about their past. That made me suspicious, so I looked through his phone (I know this was a violation of privacy, and I’m not proud of it, but I had this strong gut feeling something wasn’t right).

I found out that he had stayed with his ex during that Colorado trip. They were still in regular contact at the time, chatting often — even though he told me they had broken up 3 months before he met me. Based on their chat history, they stopped talking about 5 months ago, which is 2 months after we started dating. So, while there’s no clear evidence of cheating, I feel very misled.

From the beginning, I’ve felt like I was being kept at arm’s length emotionally. His affection in the early stages of the relationship now feels less genuine. This situation confirms some of the doubts and uneasiness I’ve felt from the start.

I still like him a lot, and I’m not necessarily looking to end things — but I’m also not okay with how this was handled. I don’t know how to bring this up to him without it turning into a fight or being dismissed because I looked at his phone.

Would appreciate any advice on how to approach this conversation and how to process what I’m feeling.

TL;DR