My gf doesn't know I stutter

My gf doesn't know I stutter My gf and I have been dating for approximately a year and few months now and I didn't tell her that I stutter. When we met I asked her out which to this day idk where I got that confidence but god was on my side I didn't stutter much, I stuttered like any person who's scared (feeling awkward). So she didn't think much of it. Like any professional stutter I developed a tricks to mask my stuttering to an extend, omitting words or asking small questions stuff like that. I've been pretty much doing great but she recently saw a video on Facebook about a guy who stuttered she laughed so hard I got curious as to what was she watching and she showed the video, she couldn't even talk. I just couldn't bring myself to laugh at all. She asked me would I keep a straight face if I ever came across a stuttering person. I felt myself turning blue with fear. I'm scared now cause since that day I can't hide my stuttering anymore I just can't for some reason. I'm actually afraid she might find out that I stutter and idk what's gonna happen. I've been made fun of at school, pretty much strangers laugh at me when i ask for direction. I'm currently studying at a university with no one who knows my past. Any advice on how I should tell her...I mean eventually she's gonna find out