Never make someone a priority if they only consider you an option.
Some friendships last for a lifetime. Some friendships last for a long time. Some friendships only last for a time. The ones that last the longest are those in which give and take, weakness and strength, have been something of a fairly even teeter-totter throughout the life of the friendship. When it becomes consistently one-sided, it's time to back away. There are others who need you more.