I only really do it for family because I know it would horrify my mum and dad. If they weren't alive, I probably wouldn't give a shit.
Going to mosque doesn't bother me, its a few minutes out of my Friday and doesn't mean anything to me. The annoying thing is when the conversation turns to Islam and I can't say what I want to say!
Well, aliadiere, I guess its best to tell your mum & dad, even if it horrifies them. My mom isn't an apostate, she's a nominal Muslim & she too was scared that it would horrify her parents when she tols them she was seeing a non Muslim & was planning to marry him, but then people whom you love & respect shouldn't be kept in the dark forever either.
Your mum & dad are alive now, Inshallah they'll live for many, many years & you'll enjoy having their love, company & support in your life for many years.
But living a lie as big as this is like living with a noose around your neck. Try to bring up the subject slowly, carefully & go one step at a time. Most probably they'll be very disappointed & perhaps wonder what they did wrong, whether they should've brought you up more strictly, but its really disrespecting them to think that they'll not get over it.
The other option is pretending now, when you're married, when you have kids, as they grow up...a lifetime of pretense, deceit & hypocrisy.
But you'll probably always have to hold your tongue a bit with friends & family-even if you can diplomatically get your view across once in a while, because they're all going to still have their Islamic beliefs intact & unless you want to be a pariah by holding views diametrically opposite to theirs & upsetting every conversation, you'll probably have to keep silent sometimes.