Sorry to introduce a note of grim reality into such a romantic discussion, but I believe that "making hay" is a euphamism for having sex. Despite the fact that there were many tarts (prostitutes) available in the area. Mount Street Bridge (on the Grand Canal) was/possibly still is an area where these ladies were available for business, he wasn't getting any.

The notion that the deep ravine is something to do with the statue seems a bit far fetched to me, although a statue of the passion does exist between Grafton Street and Clarendon Street.