So I have this black blister on my foot. I'm freaking out cause my bf said it looks like a blood blister and it can kill you. Is that true?

Dry blood. When a blood blister dries, it usually turns black. But if it is moist and black with redness of the surrounding skin it may be an infection. Infections can be serious when bacteria get into the blood. In such cases the symptoms include fever, chills and pain. Oral or IV antibiotics are used when this develops =medical treatment.