A straight guy has only one option when it comes to penis, it is attached and you get the luck of the draw. Some straights will allow themselves to look at other guys junk and may even get turned on. Some straights will secretly find a very well hung guy to service and allow a homosexual desire to control their actions under very controlled conditions.
All totaled, the straight guy needs to keep a woman available for his pleasure or pleasure himself and be satisfied with whatever limitations these situations bring. Sexual fluidity will only complicate heterosexual relationships but it seems to be trending for many guys. It all starts when your attention starts to deviate from your own penis but a good woman can keep that focus where it needs to be in order to maintain a healthy heterosexual outlook.