Sexual needs

Hello I'm 23 (M) and I'm publicly out as a pansexual and my girlfriend totally know it and is ok with and it's been 8 months since we are together and everything is good and even on a sexual plan but since a month I really can't stop thinking about having sex with a men (I'ma bottom so not the same thing at all) and this idea don't go away it make me obsessed and idk what to do anymore I won't do anything cause I'm loyal to her but what should I do? Should I tell her? Cause idk how she will react if I told her I'm frustrated because of that even if I really really love having sex with her