I'm sure someone with more experience will chime in soon, but until then, I'll just tell you that mounting = dominance behavior. he's not gay. just let it go on, he's establishing himself as head piggy. It won't go on forever! females do it too, when introduced to new pigs. have you been to
Index of / ?read the sidebar info, esp social life/introductions.
good luck! hang in there, they'll be fine!
make sure baby piggy has somewhere to escape to, though. take advantage of his small size--tuggles won't be able to follow him into a small opening.