I travel often for work. i find that intense anticipation for sex with my wife when i'll see her again often affects my erection negatively. normal?

Yes: The male sexual response reflects a dynamic balance between exciting and inhibiting forces of the autonomic nervous system. The sympathetic component tends to inhibit erections, whereas the parasympathetic system is one of several excitatory pathways. Anything that causes anxiety or excitement may negatively affect the quality of one's erection due to overstimulation of the sympathetic system.