No, continue to live in sin

"No," you replied. "We don't intend to marry and Valentine would deliver our child out of wedlock. However we do intend to raise our child or children together."

"Why not marry her?"

"I want to knock up a whore like her, not marry her. And she understands,"

There's the reason that you feel that you don't want to tell your grandfather. The simple answer was, you're a romantic, at least you believe yourself to be. You're not sure whether you love Valentine. Yes, you love fucking her, you do respect her to some degree, and you are willing to work with her to raise the children. However, what you can't promise is to commit to each other. You feel that the marriage is to be reserved to the one that will be your real wife, someone that you would love with your heart.

Also, there's the part where Valentine was popular. Yes, you're proud being able to fuck her, and you're double proud and honored that Valentine was carrying your child. But, there's the hard fact that Valentine had sex with a lot of guys, even if many of them were part of her stint as a porn actress. That mean, there's a high chance she had seen and felt longer, bigger or even both, dicks than yours, and had enjoyed better orgasms from other men. On the flip side, she probably had worse, so you may end up average, at the very least. So, even if Valentine loves you, which she has yet to do, your equipment may always be compared to those other 200 guys. It’s not impossible to love each other and sexually satisfy each other, but it’s not making it easier, either. Even if Valentine says that you're the 'best', it could be because you're rich, instead of you really being the best.

So why bother going through the ceremony, with all the expensive rocks and metals if that simple facts aren't achieved?

Besides, you enjoy the taboo of fornicating with her too much .