I have come across the above text and after looking at the translation, I discussed the meaning of 'intensidade' in the source language with a friend of mine who is a Portugese-Brazilian native speaker. He was kind enough to explain me the context of the statement.
And so, I may say that:
'Intensidade' refers to a feeling of a strong love towards a person, or a strong love present in a friendship. I would suggest that 'intensity' may be translated as 'strong'.
Not intensity is what makes one feel alive but rather strong love. If we use 'intensity' here, I believe the message is being restricted.
Well, when we have such a short text we should try to stick to the general meaning as much as possible, avoiding subjective interpretations.
I don't think that "intensity" refers only to emotions or feelings. An intense life may mean a busy, lively, active life regardless of love.
I agree with you that the first thought would be about love, but since we are not sure, I accepted the textual version because it perfectly conveys the original.
I hope you agree.