AITA for kicking my boyfriend out after what I found on his phone?

I (22F) have been with my boyfriend, Ethan (23M), for about 8 months and we’ve been living together for about six months. I thought everything between us was solid. We had our little arguments like any couple, but nothing major.

This weekend, I borrowed Ethan’s phone to look up something since mine was dead. This wasn’t a big deal since we’ve always been casual about using each other’s phones. When I opened the phone, there was a message from someone named Lila.

It read something alone the lines of “I miss you and I can’t stop thinking about you. Let me know when you’re free.”

I felt sick. My hands were shaking as I scrolled further. There were more messages. Some were flirty, others more emotional. It went back all the way until 4 months ago. I remember that day as the worst day of me and Ethan’s relationship because we took a 2 week long break from each other over something completely unrelated.

I confronted Ethan that night. At first, he tried to act confused, asking, “What are you talking about?” But when I mentioned the messages, he didn’t deny it. He didn’t even apologize. All he said was, “Why were you even looking through my phone?”

I told him to leave, and he did without much of a fight. That was three days ago. I thought I’d feel relief, but now I’m just angry and confused. I keep wondering how long this has been going on, or if it’s even over.

His friends have been weirdly quiet. One of them texted me yesterday, saying Ethan just needs “time to figure things out.” Figure what out? He’s the one who cheated so why am I the one feels like shit. I just need help.

AITAH?