The Relationship between Roz and Lil. Their sons are only an extension of their selves, so when Lil and Tom sleep together, it's like Roz says to Lil : I am giving myself to you. One forgets one's self for the other, regardless of consequences. The marvelous close-ups of their faces when they speak to each other serve as some kind of hommage to Bergman's Persona, which leaves no doubt about the message of the film. Mutual adoration between Lil and Roz. Very powerful. Loved it.
You're not a vegetarian, are you? I've never met a vegetarian I liked.
Because they weren't lesbians. I sensed no sexual tension between them. I think both the book and the film made it quite clear that their love was 100% spiritual and intellectual.
By the way, just wanted to share a new discovery I made while rewatching the film and which makes me even more certain of my theory: the single-shot sequence where Lil pursues Roz on the beach is, without a doubt, a reference to the same scene taking place in Bergman's Persona. Such a poetic shot, in both movies.
It also made me think of that film! I found the whole idea rather incestuous, that was my take. The women are like sisters, already like family. So including the sons would be tat as well.
Actually I hadn't thought of that but now that you mention it I can see a few similarities.
Of course, the guys in Y Tu Mama Tambien grow up over the course of the movie. It's questionable whether Tom and Ian are any wiser at the end of the movie than they were at the beginning.
Despite the sensual nature of the relationships between the sons and mothers (and let me tell you, as a guy, this is great fantasy) I felt like the entire film was basically a telling of the epic love story of Roz and Lil, with their children, and later even grandchildren, being used as further metaphors and extensions of that love.
You made a perfectly sensible conjecture, to which I responded with an intuitive and understandable model to serve as its framework. Allow me to elaborate:
Let ~ denote the general emotional relation between two individuals in this movie. For all characters A and B that we are considering, ~ has the following characteristics:
1. Symmetric: A~B implies B~A They all share mutual feeling. There was no rape.
2. Transitive: If A~B, B~C then A~C This is your proposition.
3. Reflective: A~A The sons are driven by their own desires and emotions, the mothers are less so but only due to the appeal of self-serving ethical superiority, not altruism ("they are so pleased with themselves"). In logical terms: if A~B, then B~A (by symmetry - property 1), together this means A~A (by property 3).
From these basic properties, the following deduction is possible:
Liz ~ Tom ~ \\\\ ~ => Liz ~ Roz and equivalently Tom ~ Ian. Ian ~ Roz
You can see from the symmetry that the two sons also share the same connection their mothers do. Visualize this by a square like above. We can generalize this further: Ian and Tom's daughters would be the two new vertices and together they form an octahedron. It can be shown by induction into future generations that the space of ~ relation is a lattice with an octahedron as the unit cell.