Looking through his phone

So I have been with my boyfriend 3 months and yesterday I happen to have the curiosity to look through his phone. He fell asleep right next to me on the couch( were 18 btw) and I see how messages from messenger were deleted with some girl from his school. I ask him about it and I stay totally shook and he says it’s nothing and that he’s telling me the truth and he told me their conversation. So me being me I ask for a screenshot and he sends it to me today and says that that girl deleted it. It was from feb 12. I scrolled up and he had flirted w her in the past which I can’t trip about but just the fact that he deletes it makes me a little mad. I just don’t know if it’s sketchy but my gut tells me it really is weird how she also deleted them too.. any opinions?