I do not think that Mulder trusts any one other than Scully. He s very solitary. She is the only one who takes him seriously. I don t know if they re in love. In a way their relationship is deeper than that because they cannot live without each other.
In order to be able to give a girlfriend the amount of time she deserves you would need time and I just can't give her that. So rather than being selfish or stupid enough to go into a relationship it's just been easier to be single.
