“Why am I with someone?” That question has to be asked. If that question has been honestly asked and reasonably answered, then you cannot go wrong, whether you marry or not, whether you remain with someone or not.
And mind you, these are not really permanent decisions to be made. This is not something that gets edged in stone. There might be a phase of life when it is really important, even holy, to be with someone; and then comes a time when it is better for both of you to grow a little independently of each other.