I'm not sure I understand the request? You want us to make the guilt go away, but I see a person who will only truly listen to yourself and what you believe. That's fine, there's nothing wrong with that.

Well here's what I think. You want your children to be better than you, so you want to marry a white girl right? I'm in a similar position. I'm half Native American half mixed White. Now I've got two options, go for Native blood as it is endangered, or go White. I want my children to be better so I am definitely going White. I know you said you feel the white race is in danger of dilution (my perception is a little different as my benchmark comparison is the Natives) but I don't believe the white race is going anywhere. Other races have taken to things like skin whitening creams and cosmetic surgery. We're technologically coming toward genetic manipulation. Humanity will definitely be preserving White genes. And unless the West loses a great war (unlikely) being white will continue to be valued. Now all these thoughts are in no way a thesis about the probable future of Race, but I am willing to bet everything on White maintaining it's standing.

As for the guilt you'll feel if you have children with a white girl, that probably won't go away. Someday your kid will get more tan in the summer than the other kids and you'll be reminded... But this isn't just about you and your kids, but also their kids. And blood washes out pretty quick. I'm half/half and I'm white enough to blend in. Your kids will likely blend in. Your grandchildren will be indistinguishable.

TL;DR, Do what you believe to be best for your kids. Your guilt over maintaining the white blood line isn't as important, theyre not leaving.