my boyfriend watches porn!😕

I was aware that my partner has the occasional wank and watches porn when I'm not around. But the other night we got on to the topic of it and it's been a fair bit more than I thought and I'm a little upset about it if I'm honest. 
He doesn't do it when I'm around so do I have a right to get upset? I just don't like the thought of him watching other women and getting aroused by it. 
Am I overreacting or am I right to feel this way?Â