Erfriert means "freezes" or "is freezing to death." It's a strong, evocative verb that goes beyond a simple "cold."
In the song, Howard Carpendale uses it to express intense emotional pain, singing, "weil mein Herz heut Nacht erfriert wenn du nicht bei mir bist" (because my heart freezes tonight if you're not with me). This dramatic imagery makes the word memorable and highlights the depth of his longing and vulnerability.
Howard Carpendale sings about how far he'd go to keep someone he loves close. He has something to admit, and whatever he calls just theory, she still gets under his skin.
The chorus is the heart of the song: she's the last thing he'd ever want to lose, the one thing he'd never hurt on purpose. His whole world stops when they're together, and his heart goes cold at night when she isn't there.
In the second verse he finally asks the real question: is her heart still open, or is there still a chance for them. The repeated "Du bist das Letzte" hook (literally "you're the last") makes clear this isn't about giving up. It's a plain, direct declaration that she matters more than anything else.