Do I have the right to be mad?

So me and my boyfriend had a break almost 3/4 weeks ago due to him being an asshole towards me, but we’re working on things and we just found out that he has ADHD (we have just had a baby too so things are a little stressful). Anyway I was dropping him off at work and he was going through his phone to call his boss to tell him he was running late I just glanced at his phone and saw multiple numbers - girls. He has no girl friends and no work colleagues so he obviously got these girls numbers when we was on a break or recently. I asked him who is ‘Sarah’ and he just looked away and didn’t say anything, wouldn’t let me touch his phone or anything {didn’t have time to talk about it since he was super late already}. Now I don’t know whether he’s cheating on me or if he genuinely forgot to delete their numbers. What do you guys think am I over reacting?

/ we had this issue when we first got together him having girls numbers and texting. But hasn’t done it since now we both go on each others phones know passwords etc but also allow privacy.