I'd say もっと見る likely than not, yes he was a virgin. He wasn't just in 愛 with Lily, he was totally absorbed によって her. She was the reason why he even was alive. That combined with the fact that most people found him to be unattractive and unapproachable I think would keep him a virgin.
But if he wasn't then I think like
link said, the most probable time he would have done it would have been between the time Lily broke their friendship and he found out Voldemort's plans for the Potters.