Saw a message on his phone which made me really sad

I’ve made a really stupid mistake.

For context, I (M20) do not agree with looking through phones it’s an invasion of privacy which is well deserved in a relationship. I do know however, that my boyfriend doesn’t really share my opinion, or more so just doesn’t really care, he’d let me and would expect me to let him. I don’t mind at all, I don’t have anything to hide.

Today though, he left his phone at home. I couldn’t help myself. it goes against my morals and it made me feel gross, but I had a quick peak at his messages and saw that he had messaged his ex relatively recently.

He and this ex are on good terms. Do not talk often though. just left everything well I guess I don’t know I don’t ask too much, I know they were important to each other at a time. He had sent a message wishing him all the best, along the lines of “I’ve been thinking of you and how you’re doing, im glad you’re doing okay on your own”.

I feel sick to my stomach. I don’t know what to do because I know this is completely and totally my fault. That message is not bad. He hasn’t done anything wrong. The simple notion that he is thinking of him makes me feel so so upset I am shaking so hard I can’t walk. We have had a few conversations about this specific ex that maybe weren’t completely resolved in the past, which could be part of it, but im just so angry at myself for invading his privacy and ultimately ruining my own day. I don’t know how to just be normal when he gets home.

I am extra torn up about it as we bumped into another ex of his at the shops yesterday. Another on good terms that I have had some uncomfortabiliriea with but also had no resolved conversation about how I was feeling. I’ve never met her. She ran up to him, hugged him asked how he was, while I payed for my things. I didn’t say anything because I didn’t want to awkwardly interrupt, but I waited for an introduction. nothing. I didn’t talk about it because im not owed an introduction, but my god it made me feel awkward and unappreciated. How do I stop overthinking and overreacting about things like this. Any help at all would be appreciated, I hate hate hate being as cold and jealous as I feel I just want to be healthy.