"If you quit getting in our way from here on, we could let bygones be bygones, I guess." "You're being awfully generous..."
Literal
Any-more we [gen-の] interference [obj-を] don't-do [if-なら], until-now [gen-の] things [topic-は] water-on let-flow-[for-you-てやる] [even-てもいい] [though-けど]? / Strangely generous [explanation-なんだな]...
水に流す (lit. 'to let flow in water') is the fixed Japanese idiom for 'let bygones be bygones' — pouring past grievances into a stream. ~てやる is the giving auxiliary used when the speaker is doing someone a favor, with a condescending or self-important flavor compared to neutral ~てあげる. 水に流してやる = 'I'll do you the favor of letting it go.' ~てもいい ('it would be okay to') + final けど trails the offer off rhetorically. やけに is 'unusually, awfully, suspiciously.'