I actually watched a Human Sexuality Lecture online from a very prestigious university in which this is discussed directly.
Turns out that this is the fastest growing area in the adult industry. Research was pulled together in a study on what people search for, their orientation, sex (M/F) they did eye tracking (people looking at images and the computer registering what they looked at and how long).
Men are by nature visual creatures. The top five list of anatomical parts that hold the most interest for men (measured by the number of times and the length of time looking at each and this subconscious computer measured eye movement) is;
2) Male Genitals
3) Buttocks (gender neutral just as much male as female)
4) Female Genitals
Turns out that this is 100% completely normal male human visual responsiveness regardless of orientation. You are not alone but, the willingness to discuss it shows that you are more in touch with yourself than most men.