Is my boyfriend cheating?

So we've been dating 7 months? And for the past two weeks, he's been hanging out with a group of friends, and there's one particular girl that he hangs out with. I've talked to him about her and he says he'll tell me when he hangs out with and even ask me for permission. I let him, because I trust him. But for the past week, he's been messaging her a lot. I also know that he calls her during the night, which he USED to do with me. And he also hangs out in Dunkin Donuts with her in the mornings without telling me. I know because someone told me. He talks to her more then he talks to me? And recently he's just been more sexual and not too considerate of my feelings. For example, he's just been trying to do sexual things lately instead of actually trying to talk. Also at night, when I ask to do our daily skype call, he suddenly started listening to music at night and can't. Should I assume he is cheating? We're both in highschool.