Pantheon Vs garren Help

Whats up guys, panth main here. I am trying to carry with panth and so far it been pretty good. I like destroying top lane and then jumping around the map when my ult is up. However it seems that if you lane against a decent garren he will just stack hp/armor. I mean unless i F blood him or win a 1v1 early its going to be a farming lane. Which isn't necessarily bad but if my bot lane is getting wrecked because of a good jungler then there isnt really anything i can do. Like right now i was pretty much even with garren cs/kda wise and i had to make a choice. Sit here and try to farm/get tower. Or back and ult bot? BTW we the enemy team had a fed xin who was farming well AND getting kills. So when i would shit on garren get him to half hp or so.. I Would have to back cuz xin would come running. Garren heals up.. and then im stuck top again and xin goes and roams. Lol it was a sad game not sure what i could have done better. ANY advice helps! thanks !