Another girl answered my boyfriends phone?

So yesterday my boyfriend promised me that he would see me. So then later on my phone wrang and it had his phone number on it. So I answered it and then his phone hung up. So then I called back and yelled his name into the phone and this girl said this isn't him this is Kayla and I was like is my boyfriend there and I heard her yell to him your girlfriend is in the phone and then he came and I talked to him and then I asked him if he was coming because it was almost 6 o'clock. So then he sees an hour later and then I asked him who that girl was and then he said that was the girl that likes me so then I got suspicious and asked so what was she doing with you're phone?? And then he said she called me because in his phone my name is there and underneath my name said girlfriend. So then I asked him so you went to that party and you told me that you weren't going to go.( his friend invited him to a party and one of his friends brought this girl that liked him over). But then he told me that the girl wanted us to break up and he said no to her. Then he was all like don't worry I was playing it safe. So now today he was supposed to go to the beach and he called me and said that he wanted to see me today because that girl was going to be there. Is he cheating on me??