Is it ok to fancy other people when in a relationship? Watch
Oh, and benefits of at least one person being non-heteronormal - at that point you can point them out and bond over how you both fancy them.
If it's the first, no harm in finding someone attractive. Usually my boyfriend and I will point it out to eachother, and then agree or disagree... :-P
If it's the second, then yeah, it's not good.
best thing is when you both find someone hot and can joke about it that way, just dont act on those feelings even if theyre inevitable