Search Results: moving on after a break up divorce

So, here's the deal. I grew up on a large public housing estate, with my single mum, an elder half-brother, and a younger half-sister. All three of us had different dads, but none of us ever really knew anything about our dads- I don't even have my father's name on my birth certificate. We went to play in the local park quite often, and I'd go off on my own- there, one day, I first met a really nice, gentle, friendly and pretty girl who was about the same age as my little sister (3 years younger than me), and the next few summers, we'd play together in the park. We ended up reuniting when she started going to the same secondary school as I did, hit it off, and quickly became an item- we even kept the relationship going long-distance when we went to university and got our degrees, we took each others' first times when she turned 16, and neither she nor I have ever have sex or had a relationship with anyone besides each other. I love her with all my heart; she's the most gorgeous woman in the world to me, and I can't even imagine being with anyone else. But when her mum died in a car accident last year, I found out from my mum (who I hadn't had contact with for a fair few years, after moving out) that she had history with my GF's mum- as the woman who'd had an affair with my dad shortly before I was born (the reason why she'd broken up with him, and why she'd left the father's name on the birth certificate blank). And investigating that lead, while my GF's dad divorced her mum when she was only 4yrs old, and he never bothered to remain in contact with his daughter or ex-wife (not even attending the funeral), I confirmed to my horror that my dad and my GF's dad are actually the same guy. We're engaged, planning to get married once we've saved up enough to pay off the mortgage. And we've had unprotected sex so many times already- it hasn't changed the way I see her or feel about her. What should I do- tell her, or bury this info deep and take it to my grave?