Loads of this, usually unintentional, between Edward and most other males such as Jacob. One assumes that Stephenie Meyer was unaware of the implications of biting pillows, breaking headboards, and Carlisle selecting a handsome teenage boy as his "companion" in vampirism (rather than say, a pretty woman).
The Romanian vampires, Vladmir and Stefan. Not only do they live and travel together, but they finish each other's sentences.
Believe it or not, Stephenie Meyer's joke story "Breaking Down" included Mike leaving Bella for Eric.
The Volturi. Primarily because the leaders are a bunch of Greek and Roman dudes who all constantly hang out together in lieu of their wives, who are barely mentioned. Aro in particular, considering his obsession with Carlisle and the fact he murdered his own sister to keep her husband, Marcus, from leaving him...
The scene with Jacob stripping down in front of Charlie in the woods is filled with this.
A fair bit between Aro and Carlisle. As mentioned in Fan-Preferred Couple, they used to live together and Aro seems very, very fond of Carlisle and his family, to the point of obsession. Aro is apparently married to woman named Sulpicia, but he barely mentions her and is never seen interacting with her, preferring the company of his male companions, which once included Carlisle. Carlisle himself once painted Aro as a god and protests Edward's suggestion that Aro is behind the newborn army, apparently believing him incapable of hurting them that way. Aro seems rather desperate to make amends with Carlisle after the almost-battle in Breaking Dawn, asking if this will hurt their friendship at all and clearly still thinks fondly of him after centuries. Carlisle seems to respect Aro too and teaches his family to respect and obey the Volturi. Then there's the whole thing about Carlisle first meeting Aro as a relatively young vampire, with the older and more experienced Aro (who originated from Ancient Greece) taking him under his wing to teach him their ways. Not to mention that after leaving the Volturi, Carlisle selected Edward - a handsome teen boy - as his new companion.
And the whole part about Carlisle leaving Aro due to a disagreement over the morality of feeding off humans is rather reminiscent of another pairof vampires whose relationship was dripping in Ho Yay.
The Amazon vampire coven (two vampire ladies who live together in the jungle and are very close).
Alice and Bella. Their reunion in New Moon is rife with this.
In Eclipse, Leah and Bella when Leah tells Jacob that she had a dream about kissing Bella. We are supposed to see this as a natural result of the werewolf telepathy but... not everybody does.
Even with Esme and Bella. Anyone remember her calling Bella "Dearest Bella", like, right against her skin?