Jaribu,
Your grandma is a wise woman. But methinks you could be confusing between three things:
1. Marriage - this is a contract between two (or more) people to do certain things,mostly to form and raise a family
2. Love - is a psychosis. A psychological condition,sometimes fatal,that afflicts many of us at one point or other but which we usually recover from. One of the symptoms is unrealistic expectations. Marriage is a great cure for this condition.
3. Friendship - a positive relationship between two or more people,often based on shared interests. Friendship that survives negative phases will tend to grow and last longer. One of the conditions of lasting friendship is low expectations.
So which is which?
"The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth." (Niels Bohr)