No, you can love two people "differently" or for different reasons.
Even parents who love all of their children will secretly admit that they have a favorite child or one they get along with better than the others. No two people will make us feel the same exact way when we spend time with them.
Individuality and personality traits elicit different feelings and if this person was told they could only have (one) of them as their mate they would choose one over the other for "specific" reasons.
Lastly if you're "in love" with the first person you're not likely to want to invest the time needed to fall in love with the second person.