if i starcrossed lovers an enemy unit and they use retreat on it does the friendly unit still go back to hand

Yes — your friendly unit still goes back to your hand.

When the enemy unit is Retreat-ed to its owner's hand, that target is no longer available, but Star-Crossed resolves as much as possible on the remaining legal target. Per Rule 359.3.e.8, when fewer than all targets become unavailable, the instruction still executes on the valid ones (RiftJudge FAQ #10736). The returned unit also still channels 1 rune from Retreat regardless.