The player king talks about how we declare our love, and can't imagine loving anyone else, but how "what we do determine oft we break...what to ourselves in passion we propose, the passion ending, doth the purpose lose." Basically, in that passage he is saying that we often break those vows of love when the passion is gone. He goes on to state that life changes so quickly, and that "even our loves should with our fortunes change" (III.ii.196-212), saying that as our life changes, so does our love. His comments on success are that who knows if love and success, or fortune are linked, and which one comes first. And when fortune is ours, we often call friends enemies and enemies friends, so who is to say what we will do in any given situation. All of this is an indirect hit against Gertrude, and how her seeming burning love for Hamlet's father faded quickly as Claudius resumed the throne, and then turned upon the new king with renewed vigor.
The Player King makes a profound speech about “love” and “fortune” within The Murder of Gonzago (the play-within-a-play from Hamlet). The speech referred to here is specifically in lines 192-221 of Act 3, Scene 2. Although the speech is open to interpretation, the clincher is the original question: “For ‘tis a question left us yet to prove, / Whether love lead fortune, or else fortune love.” In other words, does love lead to success/wealth or does success/wealth lead to love. The Player King reveals that “love doth on fortune tend.” And further, “For who not needs shall never lack a friend.” In other words, someone who has achieved success is never in want of friends or lovers. The Player King admits that the love of the Player King and Queen seems to have overthrown this idea, but the Player King doesn’t seem too certain about what the Player Queen’s actions would be if the Player King were to die (which he does presently). The Player King is a smart guy. For even though the Player Queen has just insisted that “A second time I kill my husband dead / When second husband kisses me in bed,” she still ends up cavorting with the Player King’s murderer.
I think he basically reveals that love is just a word, four symbols put together, to point at something --- but we can rarely, if ever, agree on what it is that it points to. At the height of infatuation, we think this is what "love" refers to. But the very intensity of this passion often causes it to burn out quickly and what we thought was love is gone. When people say "I love you," who knows what they are talking about: passion, sex, self-sacrifice (greater love than this no man has)?
So often love ends ... because it was something other than love that we named "love." Shakespeare thinks that love doesn't change. In Sonnet 116, he writes "Love is not love/ Which alters when it alteration finds/Or bends with the remover to remove." It doesn't depend on passion; it doesn't depend on success. This is not to say what it is, just what it is not.