The Billionaire hitmaker admits he was madly in love with the pop star and even gave her a promise ring after vowing to spend the rest of his life with the singer - but his drug issues and the couple's separate career successes brought the two year love affair crashing to a halt.
Opening his heart in a new Behind the Music TV special, which aired in America on Sunday (14Oct12), MCCoy recalled the start of the romance with great fondness, noting, "We looked really cute together. We get (sic) along better than any other girl I've ever hung out with in my life. That was the beginning of a really really awesome time for me... When I was around her I felt really at ease and comfortable with myself... It was the most amazing thing ever."
But the star couldn't hide his dark thoughts as he admitted he tried to hide his drug use from his Christian girlfriend.
He said, "She wasn't stupid... She knew when I was f**ked up... I chose drugs over our relationship... As things started taking off for her the more I started to doubt my role in her life. There were times I felt like a stepping ladder."
And it appears he's still bitter about the way she ended the romance - by email.
MCCoy added, "It started off with 'I love you so much I hate to do this...' Someone that you are ready to spend the rest of your life with sends you a f**king email just s**ting on your whole parade. It destroyed me."
Perry went on to romance and marry British funnyman Russell Brand, but that relationship ended in heartbreak for the singer at the end of 2011. She has since been linked to John Mayer and Florence + The MAChine star Robert Ackroyd.