In the situation that you mention here, it is likely that there will end up being conflict between the two and hurt feelings on the part of at least one of the people in the relationship.
If two people are in a relationship and one of them thinks the relationship is more permanent than the other does, there is sure to be conflict. The one who thinks they have a relationship will be very upset and angry when they find out the other person does not agree. They will feel betrayed because they will think that the other person has misled them.
It is very difficult if two people do not have the same perceptions of their relationship. It is sure to lead to conflict and hurt feelings.