The German branch (English, German, etc.) and the Italic branch (Latin, Spanish, Italian, etc.) of the Indo-European languages each split off from Proto-Indo-European, their common ancestor. This probably happened There is no other relation between the two branches (except reciprocal borrowings and influence). Both come/come and how come from the same Proto-Indo-European root (probably something like **kʷo-*, ), but they went through different phonological changes in the mean time, so they look very different now.

Spanish and Italian split off from their common ancestor Latin a short time ago, no more than, say, 1500 years ago, so they still look very much alike. There was also much contact between them, and hence more borrowings and mutual influence. This does not apply to the Germanic and Italic branches of Proto-Indo-European, whose oldest common ancestor existed over 5000 years ago; and the two branches generally didn't undergo much reciprocal influence either.

A map of the spread of the different Indo-European branches, from Wikipedia. Blue is Italic, Red is Germanic. Grey areas are mostly non-Indo-European.

A chart of the history of the evolution of Proto-Indo-European, with approximate/hypothetical dates.

Probably from a paper by Gamkrelidze and Ivanov, “The Early History of Indo-European Languages” in Scientific American of March 1990.