As an adc main, I explicitly ASKED if support should help other lanes (specifically mid, but the point holds) if bot is winning. The overwhelming response was NO (I admit I'm not sure I agree) and if Bot is ahead Support should either help adc snowball MORE or build self up. It sounds like you WANT to play JG. Bard is the only supp that has a true "reason" to be wandering off that far (the complete OPPOSITE end of the map) from the adc. (as an adc, I should be TRYING to stay with you (or vice versa) so I don't die)
I can play solo Bot for a while, I'm not someone who wants supp right next to me at ALL times. But getting TP just so you can help top farm kills is silly. Top SHOULD be able to handle lane on their own, that's why they WANT Top. If they can't JG should back them up, ESPECIALLY if Bot is ahead. If you're talking after the 20 min mark, then you shouldn't need TP because everyone is wandering. Again, if you want to be a SUPPORT then learn to play with
or at least
While you're at it, learn to upgrade your damn trinket.
But seriously, learn JG, if your straight-up core mental mechanic is to get someone (be it you or someone else) the kill, then work on the role that really does only that. Support needs a LOT more utility to the team than simply setting up a damage dealer in a 2v2 or 2v1.
(And no offense intended to JG in the above, I personally hate the role because my rotations and overall map awareness needs too much work)