T.M.I. But I need your opinions!

So I'm 21 & I'm in a long distance relationship with a man I love and trust very much. 
But anyways, my best friend made me buy a vibrator because she said it's amazing especially since I'm in a long distance relationship so it'll help when I'm craving. 
​So I told my boyfriend about it thinking he would be okay with it, but he HATES it and wants me to throw it out even though I tell him that I think of him & only him whenever I use it. 
​But straight to the point, I use it almost every night after he goes to bed (because we sleep on the phone every night and he works a lot so he sleeps before me), is it bad that I'm doing this behind his back? I can't help it, it's honestly addicting & it's hard especially since I'm in a long distance relationship and I only get to see him like 3-4 times a month