Not Like Other Boys , by Marlene Fanta Shyer and Christopher Shyer. Give yourself opportunities to meet and interact with gay people. It is a way to become comfortable. Some suggestions for doing this are to go to services at a lesbian and gay synagogue, go to a gay bookstore, go to a Gay Men's Chorus concert, go to your local Gay and Lesbian Services Center, etc. Be open to your child.
Human sexuality is very complex.
The current thinking is that sexuality is either inborn or determined within the first couple of years of life. Being gay is not a phase. It is not rebellion. It's okay if it takes time to feel comfortable. Accept your many and varied feelings of love, grief, denial, anger, guilt, discovery, fear, wonder, empathy, respect for your child's courage, etc.