Is my boyfriend cheating on me?

Latisha
So I went through my boyfriends phone a month or so ago(without him knowin) and found that he had been texting a girl who's name wasn't save in his phone is was just the number, but it was a local number... she was talking about her being on her period and what he would do if she wasn't well...I was really too mad to pay attention or read what he had said back but it wasn't bad I don't think he really sad anything that bad back. Well she sent him a screen shot of my Facebook page where it had my profile picture of me and him, he replied "yea we've been talking, plus me and you are friends anyway"...well we had been dating 3 months by then. I haven't said anything to him about it I've kept my mouth shut cause we don't go through each other's phones, should I keep quiet? Or ask him about it. It don't even make me mad anymore cause the texting stoped end of July, and when she seen he had a GF. 😕 I just kind of wanna know if he cheated on me or not. 
But the texts shown no indication that they had met up and had sex even though she's local. 
UPDATE: I straight up told him about this and he said he "didn't remember" I told him everything she and he talked about because I remembered almost everything he still claims he "don't remember talking to any girl"