Hey, there, aintfoolin .. 
Your post has me walking down memory lane, too. I remember my early days discussing every nuance of BBM too. Never get tired of seeing new fans experience all the excitement of exploring what might or might not have been. I learned so much about the implications of everything from the comments of others, and I can't say enough good things about all the BBM fans who post here. 
Randall has been a source of much contension, considering how brief his appearance in the film was. Ironic, isn't it, the weight he carried was/is disproportionate to his time in the light, but there it is. 
Like you, aintfoolin, I always felt that Randall was a significant part of "the rest". Mostly because I think this was the time for Jack when he stepped over a new boundary, another blow to his relationship with Ennis. I'm awed everytime I see the look on Jack's face, that moment on the bench outside the party when Randall suggests that he and Jack get together, "do a little fishin'". This is different, it's a whole other step away from Ennis, beyond an anonymous encounter into the realm of "real" people. I always felt that this moment really broke Jack's heart. If he does this (which it is heavily implied he does), it's one more step away from his dreams of a life with Ennis; one more admission that what he most dearly dreams of isn't within his grasp.
Anyway, I think that the start of Jack's relationship with Randall was one of those watershed moments, one that impacted him through the following years and weighted heavy on his mind when he was with Ennis; "all the rest", that he likely dreaded and wanted Ennis to know, maybe. 
Your absolutly right about the forums MissG, if I may. I never tire of reading new perspectives on the threads about this classic film. Some of these older threads are simply fascinating! ..Love reading them.
I'm glad you feel as I do that Randall , even though his role in the film was small the sigificance of his relationship with Jack makes him huge. Had Jack really hooked up with Randall he would leave in his wake a road paved with bad decisions, a man he loved, who did'nt know how to commit fully to a loving relationship due to fear. A failing marrige, entered into for all the wrong reasons and all the drama these relationship entail. I think Jack found Randall's approach refreshing and new. The sense of the scene that preceded this one where they are packing to leave, You just sense Jack's thinking..".Here we are, once again packing to seperate for months at a time one more f-ckin time." "I cannot keep doing this.". His face said it all.
After 20 years, he's still drifting along. I think as he got older his perspective of his own role in the affair changed at some point, I think it had to. Started to think of what HE wanted in his maturity. Instead of what every one else wanted. .. including Ennis He was just plain tired of having his feelings hurt.
Then along comes Randall... He's different from Ennis ..but not that different. He is calm,softspoken and seems non-threatening. A married man, who was taking a chance of being the one rejected, or something worse, but he did proposition Jack, This gentle , matter-of-fact approach put Jack at ease somewhat, but as he sat on the bench, I always thought that Jack was questioning the possibilities and the impossibilities. The impications and the what ifs.
Someone wanted him for once. He was was'nt carrying the load by himself for once. This was new to Jack . Randall was on his level of thinking concerning a secret affair between two men ,not above or below it. Unlike Ennis , he had found a *comfort zone* , and had come to an understanding with his sexuality it seems. Jack had to appreciate this.
In his maturity he is aware that Brokeback was the beginning for he and Ennis ,but BB had consumed he and Ennis's lives for 20 years and it was time to take the relationship move to a more permanent level and this is when he discovers that Ennis was stuck in nuetral. Jack had no real solution to convince him otherwise. " that's all we got boy, f-ckin all"! Randall was a tall ,cool .glass of water in this transitional moment for him.
by an
I'll stop rambling now.
