Every time he uses his time machine to time travel he creates another timeline. At the end of the arc it was all for fucking nothing since after Zamasu was destroyed, Whis suggested just sending Trunks to the future again but before Zamasu attacked. So two Trunks ended up together.
The current arc brought up a massive plot hole with the Black arc. Whis easily spoke to the grand priest to go to the tournament. If angels can just talk to the grand priest any time then how the fuck did Zamasu kill all the gods in Trunks' timeline? And again in the current arc the grand priest shows Zeno what's going on in Universe 9 as Sidra is trying to recruit people for the tournament. If the grand priest can just look at universes any time why the fuck did he not notice everyone dying to Zamasu? Shit writers. Shit show.