The noun friend is a broad term that suggests varying degrees of familiarity. It can refer to someone who is on good terms with another (Who goes there? Friend or foe?), to a supporter or patron of some institution (friends of the Boston Symphony), or to a connection on social media. Most commonly, though, a friend is a person with whom one is on intimate terms and for whom one feels a warm affection. This is the meaning that gets us closest to the noun companion. A companion is a person who shares one's activities, fate, or condition. You might have a traveling companion or a companion in despair. The key difference is that a companion is a person who you are frequently in the company of. A friend may be far away, but still hold a special place in your heart.
The standby adverb always is used a few different ways. It can be applied to things that happen on every occasion or without exception (he always works on Saturday), to things that occur continuously or without interruption (there’s always some pollution in the air), or it can mean “forever,” as in, Will you always love me? The adverb invariably is a synonym for always when talking about things that happen every time, without exception. If the weather forecast is invariably wrong, then it is never accurate (and maybe it's time to find a new source for your weather info!). If an answer to a question is invariably “yes,” then it is affirmative every time the question is asked.
The adjective innumerable denotes a number that is beyond count or, more loosely, that is extremely difficult to count: the innumerable stars in the sky. A strong synonym for innumerable is myriad, which describes things of an indefinitely great number (such as stars of a summer night) or things that have innumerable phases, aspects, or variations (the myriad mind of Shakespeare, for instance). Fittingly, myriad takes myriad forms. That is, myriad functions as a noun as well as an adjective. You can say “a myriad of reasons” (noun), or “myriad reasons” (adjective). Both are correct, though the adjective form is more common.