“But it does seem that you are cynical about the existence of real love...”
No, I am not cynical about that. You just cannot know if you have real love, except in hindsight. Everyone will think, at the beginning, that their love is real, but they don’t all turn out to be right. Everyone pledges to stay faithful forever, but they don’t all keep that pledge. So saying “well if it is real love you don’t have to worry” is no consolation, because I am not a prophet, so I cannot see the future and know if it will prove to be real or not.
The song is nice, but it is just sentimentality. It doesn’t change the reality, which is that counting on love to keep a relationship together is demonstrably unreliable. Lots of people do that all the time and get burned.
People sometimes give up on the love that the Lord gives to them that is supposed to spill over into others in their lives. That doesn’t mean that there is no love, but that sin won out over the love.
The love of Jesus is MUCH, MUCH more then mere “sentimentality”.