the thing is, Exx, that suffering is included in losing... but it's to "explicit". I think "loved and lost" puts together the ideas that you loved, you trusted it was going to work, you bet on that love... and you lost! it failed, you lost the bet and the person... I mean... it's a "richer" concept...
also, of course you suffer if you loved and lost someone, but if you take out the "lost" you are merely saying "loved and suffered"... you could think that he suffers because he's in love, he suffers because he loved someone that was not right for him... I love the English phrase "It's better to have loved and lost than never to have loved at all" so I like the idea...