This is the text in question (maybe others):
As for the Wisdom who is called “the barren,” she is the mother of the angels. And the companion of the Savior is Mary Magdalene. But Christ loved her more than all the disciples and used to kiss her often on her mouth. The rest of the disciples were offended by it, and expressed disapproval. They said to him, “why do you love her more than all of us?” The Savior answered and said to them, “Why do you I not love you like her?” When a blind man and one who sees are both together in darknes, they are no different from one another. When the light comes, then he who sees will see the light, and he who is blind will remain in darkness. [Gospel of Philip]
Well, one might ask the counter question, can you think of one legitimate reason why the canonical Gospels would have made up a differing story?
Well, I’m sure you could…
The simple fact that the canonical gospels are 1st century, and the Gospel of Philip is third century, leads me to take the latter as less authoritative.
Nevertheless, I think your question, needn’t be taken rhetorically, and perhaps there are a couple of good answers.
First, philosophically, gnostics saw the existential malady of humanity as the differentiation of the sexes. The concept of the “bridal chamber” was sacramental to the Gnostics. So a celibate Jesus would be anathema to them. [See also the ending of Thomas 114 – not cited below.]
Another more form critical answer might be this:
In the Gospel of Thomas (gnostic), there is this text:
Simon Peter said to them, “Let Mary leave us, for women are not worthy of Life”. [114:1]
It is possible that Gnostic tradition preserved a gender-based resentment towards the female followers of Jesus, and perhaps even of Mary Magdalene in particular. Perhaps this tradition was turned more solid by later storytellers, either by inventing narrative to flesh out the story, or by bending the tradition towards a more gnostic view.
All one has to do is see “Jesus loved her best” as an immature reaction on the part of the male disciples (“mommy likes you best”) and allow for the “kiss” to have been added sometime over two centuries to make the story more interesting. The “blindness” was culture-based gender discrimination on the part of the disciples.
With this plausible scenario, Jesus and Mary could have been “just friends”.
Or the whole thing could have been made up out of whole cloth.