Could s/he just not keep it to themselves?
This is a common question. The best answer to this is another question - "Who would this help?"
Keeping such a secret to oneself can be detrimental to one's mental and physical well-being. It is well documented that unhappy gay or bisexual children are up to seven times more likely to take their own life, as a result of bullying and a general lack of self-esteem. Many of them drift into substance abuse or risky sexual behaviour. Anorexia and bulimia are other consequences of the increased stress of being an unhappy gay or bisexual child. The difficulties which some children experience in talking openly about their sexuality to anyone can leave them very isolated and depressed.
Given the discrimination LGBT young people can suffer, simply because of who they are, try and remember the courage your child showed by ‘coming out’ to you.