Falling in love is the east part.

to give a weak form of a disease to a person or animal, usually by injection, as a protection against that disease

not intentional

to have a short sexual relationship with someone

range

to move back slightly from something that is unpleasant or frightening

to make sth less harmful

done according to an arrangement by which you do something for someone who does the same thing for you

useful, important, or good enough to be a suitable reward for the money or time spent or the effort made

really and sincerely

able to continue over a period of time