Just because there is no obvious and rapid mate doesn't mean black shouldn't resign. Black's position is clearly lost. Two whole rooks (and two pawns) down and no compensation. Personally, if I had been black, I would have resigned earlier.
You played well by the way!
18 Rxe6 is a no brainer, and leaves him with nothing positionally or materially regardless of his response. Note ....Qxe6?? 19 Re1
You seem astute enough to know that this game was lost by your opponent more than won by you. Granted, such can be said about most any game, but more so with this one. One of the hardest mental tricks is to assume your opponent will always make the right move. If you want to improve, work against an engine or find stronger players. Weak opponents permit bad habits.
I'm not an excellent chess player, as you can see from the game, but I'm very eager to improve my chess. Here is a game with my short analysis (more like comments than analysis) that you can watch trough and give me some advice. Anyway the main question is: How to win a winning position; what should I have played if black hadn't resigned?
Thanks for any kind of tips!