Happy Mommy- it is not uncommon for one twin to pass away in the womb in early pregnancy and is often termed Vanishing Twin Syndrome. When that happens you can bleed but the baby's body is absorbed back into your body at this young age. If you were further along, close to term, you'd more than likely deliver early to prevent anything from happening to the other twin as your body cannot absorb the deceased baby.
It's no comfort to hear any of this, I know. I'm so very sorry! The little one could catch up. I wouldn't give up hope just yet but definitely prepare yourself for the possibility.
And to answer your question- no it should not affect the other twin. I know a woman who was recently pregnant with quints (5 babies!) and three of them passed early on. She is now having two healthy twins.
It is measuring 3 weeks smaller to tiny to hear a heart beat I"m not that far along yet. The dr's said it was a good possibility.
My mother was pregnant with fraternal twins and she miscarried one of the babies. My brother is now almost 18 years old! Why do you feel as though you are going to miscarry the smaller of the 2? If you need anyone to talk to...let me know!!