BAD PETER! Do you know what she does with those children? However, Peter is keeping Gareth alive at the same time so...yeah.
As they have both been around for a while they have to have bumped into each other at some point and if Peter is messing with Morgana's pirates, Gareth wouldn't hate him. Probably doesn't trust him as he is immortal but isn't actively working against him. So yeah, it should be interesting.