Hi.  Every time I see a girl I do not get an erection yet I can have a huge erection when I am by myself.  This really hurts the girl even though I find her really hot and arousing.  I can not masturbate next to her either.  How can this be fixed and what can be the cause?

Also I find when I do have an erection for her it disappears as soon as I put a condom on.