I already did a search on here for this and found a thread that sort of talked about the subject but I'd just like to share my own personal situation and see what you guys think.
I'm 19 years old and I'm in my second serious relationship. She's an intelligent, gorgeous and all around fantastic woman who means the world to me. Our sex though is... I guess very frustrating. I have a real hard time getting a good erection when I'm with her and while I make up for the lack in other ways (cunnilingus, etc.) it embarasses me, as well as making her slightly upset. I'm sure it's not her fault as I can get it up there well enough when I'm masturbating, but it just doesn't want to happen when I'm with her.
I would appreciate any ideas, tips or solutions.
*Edit: As an aside, I'm a 6'4'' healthy chinese/german guy who took a break from Soccer for a year because of a leg injury. Because of the injury, I've really lacked any cardiovascular excercise lately. Just a little info.