pressure for nudes

I love my boyfriend but for the past few months he keeps asking me to send nudes on snapchat. He travels a lot for work, so it only happens when hes away which I guess is understandable but I always say no and have even spoken to him on three separate occassions about how the idea of sending them makes me uncomfortable and he still is so persistent in asking me for them and pressuring me by saying things like 'why cant you do something fun and spontaneous for once?' and 'cmon you know i wont show anyone'. He even sends them to me in the hope he will get something in return. Ive spoken about this with my friends and they all think its pretty bad on his behalf for pressuring me. Has anyone had any experience in this situation? I dont know if I should just send them anyway because maybe I am being silly in not sending them when we have been dating for over a year... Please help!