They act out their love through partnership and respect, through trust and loyalty, protecting one another at all costs and literally going to the ends of the earth for each other. Even when, late in the series, the pair could be called lovers, they are first of all partners and friends. They form two halves of a whole, two contrasting elements working in tension and in harmony to create an effective synergy. The characters, as the show itself, is noticeably lacking when one half of the pair is missing. Together, however, they are formidable, and more than the sum of their parts.
The dynamic between Mulder and Scully of opposites attracting, or more importantly, working in conflict and yet in harmony, is not just an aspect of romantic love, where the male-female pairing is most often emphasized. This is an element of their friendship and partnership, and therefore reflects both what the two genders can contribute to one another beyond simply procreation or a sexual relationship, and also what any two human beings can contribute to each other through their differences. Mulder and Scully each bring something to the partnership that the other lacks. Scully contributes cool-headedness to his impulsivity; Mulder adds spontaneity to her reticence. She provides a foundation of weighing evidence and establishing provable facts, while he has the imagination to think outside the box and make intuitive leaps. Although their differences lead to many arguments, the pair uses this in the positive sense of arguing one side of a case and thereby reinforcing it, rather than allowing their disagreements to become merely fights. They let their differences and their contradictions combine to become their greatest strength.
What Mulder and Scully have left, without the FBI or their mutual fugitive status, is their commitment to each other. “Don’t give up” is the essence of commitment: refusing to give up on a person or a relationship even when common grounds have been stripped away, even when the individuals have changed or grown apart, even when there are disagreements, when the only reason to stay is the commitment itself. This is the true constancy of love, not in the persistence of an emotion, but in the choice to make and honor a commitment. For Mulder and Scully, the end of I Want to Believe is a renewal of their commitment to one another, the decision to move forward together to face whatever may come. Their connection to each other, face to face (or forehead to forehead), is alone what now defines them—friendship has become eros.