Is it normal for a girl to get upset over the fact that her "boyfriend" is spending the night with girls?

so me and this guy have been "dating" without actually dating for 7 months. he lives four hours away and is 4 years older than me. he likes to spend the night with girls and he is really cute. he could have any girl he wants. he always tells me he loves me and that i am the one for him and we talk throughout the day everyday (around his busy army schedual) but for some reason when he spends the night at girls houses it just pushes buttons on me that it shouldnt. i have talked to him about it and he doesnt see the problem his response is always " you are the only one for me i promise nothing is going to happen.. they arent you are they" should it still bug me that he spends the night with other girls or what????