Aunque means "even though." Aunque tiempo ha pasado, todavia pienso en ti" means, "even though time has past, I still think of you."
Jamas means "never again." or "no more." "Jamas voy a fumar" would mean "I'm not going to smoke anymore."
Inalcanzable means unreachable. It's from the verb alcanzar (to reach). I can be used in the sense of an unreasonable goal or a person that simple cannot be "reached." Note that this just slightly different from unattainable but there's a separate verb for "to attain."
Pro supesto means "of course" or more colloquially "for sure" as we would say in english slang. "Is it really going to happen?" can be responded to with "por supuesto que si!" or "of course it is!." "For sure it is!" It doesn't always have to be so upbeat though. For example, "Of course, no one really thought it would happen that way" would also start out with por supesto.
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