the Parker day 7 thing is Parker trying to stop Gil and Lars when he mistakenly thinks they're fucking in the restroom while Lars is actually vomiting. Gil thinks that he and Lars having broken up is a good thing. Gil makes it sound like a mutual decision, but it's possible that they were still dating when Lars disappeared and this hurt Gil. They had already broken up months before the vn started. The same wrong decision thing could either refer to getting back with Lars, or whatever mistake Parker made that he doesn't want anyone else to make.
the thing about Parker being why Gil is still a virgin could be partly a joke, like instead of being intentional maybe whatever came up that caused Gil to cancel his plans with Lars was Parker needing Gil's help with something (which could also be the night Liz put a missing persons report out on Parker).
as much as I complain about how Parker treats Gil and worry about him doing so outside the bounds of their agreement in the past and/or future, Gil did ask him to do so.