Is it true, when you question whether you love anybody . ?

Is it true that it mustnt be true love if you have to question it? i saw something in my sisters room about her fiance, she had written down questions like " do i love him?" "do i want him in my life forever?" and all sorts of questions like this. so what do you think? does she love him or is she settling for him? the wedding is in august this year. my bf was chatting to my sisters fiance and her fiance admitted that when he first met my sister, it was her friend he was interested in. he also has said that he used to use girls a lot. the main worry for me is that the marriage wont last as he proposed to her when he was drunk and is taking no interest in the wedding at all! my sister is 27 and her fiance is 30.
Answer
I think its normal to question your decision its a big commitment that changes your life forever..i know i questioned how i felt before i got married and i believe i made the right choice..im happy and loving life..id be more concerned about him not being interested to me that may sound a little dodgy..at the end of the day only they know how they truly feel about each other..speak to your sister and she how she feels about the whole situation