erectial problem

Most of my life I have had a normal sex life.  During my early years I would get bored easy so I would cheat or go find a prostitute or watch a lot of porn.  I am in my early 40's now (and in my 30's with other normal relationships) I have had a fear of getting/maintaining an erection.  I currently do use viagra which helps however when I get an erection I seem to ejactulate very quick.  I dont feel i really need the viagra since I can masterbate whenever I choose to.  I believe it is some type of mental fear.  I just want the normal sex life with out the fear of losing or even maintaining it.  I know that when I get erect I want to get right into the act because it seems that the feeling of intercourse or oral on me helps maintain the erection.  During fore play with my girl I seem to lose it and I need her to do whatever to get me erect and then go immediatly into the act.  I feel bad for her cause it seems like I am not turned on by fore play or even when I preform oral on her.  She is beautiful and I dont know why I have a fear.  I feel as though I need to use the viagra because it gets me erected quick where as if I dont use it I feel that I may not get erected which I usually dont.