Cheater?

My bf and I haven't been spending that much time together lately and when we do it's always for like 30 minutes and then he has to leave. He's also been hanging around with a girl who loves to get around with guys (if you know what I mean). He's also been getting a little bit to close to her but as soon as I bring that up he says that he has to leave. He also won't even let me see his phone to read their texts. Should I be worried?