Haven't we all encountered that "Oops!" monent at one time or another? Maybe not to that extreme...but still. It had been 6 months so that doesn't surprise me at all. What does surprise me is her reaction! She ruined what still could have been a wonderfully erotic evening and I don't blame you for getting dressed and walking out. She didn't deserve your attention.
Had she reacted in an understanding or even humorous way, you could have reassured her that it was the circumstances and her sexiness that caused your extreme state of arousal and that she should take it as a compliment. Then, you could have showed her how a real man can please a woman in ways that don't involve a stiff cock (at least not right away!)
Of course, if you are anything like me, giving her a full body massage while you explore her body's most intimate areas, followed by oral and digital ministrations to those same areas, would keep her happy and soon would have had your cock standing at full attention and had you ready to redeem yourself and your pride! (Not to mention the fact that most of us can go on a long, long time the second time around!)
Seems to me that she blew it, not you!