Who said that love doesn't last forever

Today I was coming out of work when I look to my left and I saw the most beautiful scene,like almost out of a movie.An old couple that looked like they were in their seventies walked right by me holding hands and smiling like they were two young souls in love for the first time.I asked them how long have they've been married for and they said for almost 50 years.My jaw fell as I started getting this warm feeling of innocence from the spoken wisdom and mutual Love those two had:)