When I was 13, I got caught messing-around with a friend from down the street. He and I had been playing around for about half a year at that point. We had our hands down each others' pants, and his mom walked in on us. She walked me home and informed my parents of what she'd found.
My family was a pretty traditional Catholic family, as was my friend's, but his mom was a psychology RN, so she was pretty well-informed, considering that it was 1990 in the deep South. Mom and Dad were visibly upset, and sent me to my bedroom before they continued talking to my friend's mom. I eavesdropped from my bedroom door, hearing her tell them that experimentation was normal, and that it might not have meant anything regarding my (or her son's) eventual orientation.
After my friend's mom left, Mom came into my bedroom, calmer, but still stone-faced. I still remember her exact words:
"your father never wants to hear anything like this about you ever again."
She then exited the room, telling me nothing about how she personally felt, asking me nothing about my thoughts. That was the last that was spoken of the incident.
I never hung-out with that friend ever again. I withdrew to myself a lot, actually. I made a decision to not date any girls, as I already knew I was gay (I'd already gotten past the "'maybe-I-can-pray-it-away" phase), and I didn't want to send them any mixed signals or give them any false hope. There were many moments in high school where I wondered if I'd ever be able to come out to them, or if they'd ever accept me. Hell, those question marks hung over me well into college.
I don't know what changed, but something did while I was away at college. Mom would ask me if I was watching Will and Grace. Or if I had seen the Ellen coming out episode. She asked me on the phone if I'd read about Matthew Shepard (I was at college in rural Mississippi, so I'm guessing that she was worried). But she'd always find a way to bring it up.
I didn't come out explicitly at first about my relationship with HylianGreg. I just always ended-up bringing him home. And we'd be honest about our boring lives. Saturday night in college watching an Antiques Roadshow marathon! Going to Greg's sister's wedding. His step-dad's funeral. Us taking the nieces & nephews to the zoo. My bet was correct: Mom & Dad just figured it out and accepted it along the way, no drama.
When we moved back to New Orleans from Texas, it got just downright boring. Normal. Dad had two new fishing buddies, and Mom had us to take her to the theatre. My sister had a wedding, and Greg was in the family photos. And we'd all be able to go to football games together (man oh man was Mom relieved that Greg loves football. I think not liking football would've been a bigger issue than the gay thing!). After worrying myself sick over this through pretty much all of high school and into college, Dad especially was surpising me. He'd start asking, "where's your other half?" or "where's your partner?" or (about our dog) "where's my big guy?" It was suddenly no big deal, and now he'd get disappointed if I went home without Greg.
Dad had surgery recently, and I had to babysit him at home. In his drugged/teary state, he told me that he was glad that he'd "won" another good son, and that he's glad that I'm settled and that we can take care of each other. Made me cry (hell, I'm teary-eyed now).
I guess the main takeaway is that even if it seems probable that Mom and Dad will react harshly, it often doesn't stay like that. People change and grow a lot over time, so don't lose hope.