According to Temple ( acknowledged expert in all things lovey ) these locks symbolise the bond between two people; each takes one of the keys as a momento and they leave the lock attached to something. In this instance the Lagan footbridge.
"Lend me you hand and we'll conquer them all but lend me your heart and I won't let you fall WORD WORD WORD"
Seems to be a corruption of the lyrics to Awake My Soul by Mumford & Sons. They are apparently now very popular in the USA and it seems that Mr Mumford is found by the ladies to be a pleasant sight.
"Joe, I like you a million times more than Electric Picnic... every day! I like you WORD"
Electric Picnic is a music festival which is held annually in County Laois. Apparently. I assume that it is like an airshow, but with bands instead of aeroplanes.