So this is a broken relationship in a line of many other broken relationships before; he knows this feeling of loss very well, it’s not the first time:
Same old empty feeling in your heart
Still, he starts every relationship with all the enthusiasm of the first time:
'Cause you loved her too much
And you dived too deep
So basically, this is a song of a romantic man deep in sorrow who is just wondering why he can never find his true love... and keep it.