When you think of the beta: don't think of the romantic guy who knows what, when and how to do the right thing. Think more of the outcast, strange and unfit teenager who is hopelessly in lust with a bitchy cheerleader, labelling this 'love'.
There is a guy I think we may all know: perhaps he's a friend, or perhaps he's an acquaintance. Perhaps it happened to you or perhaps it happened to someone else. He will not give up. He will be there; he'll wait until you think he's given up but he hasn't. You will move countries, forget to take contact details and he will find you, possibly following you. Sometimes you feel like the lines into stalking may have been crossed. He will remain your friend, and you will have to be a complete and utter unsubtle bitch to get rid of him. He will take care not to cross that line. He will repeatedly reassure you of his affection, be the first to rush in at the remotest hint of emotional vulnerability, be the first to scoop you up on any rebound by being a 'nice guy'. He will think of himself as your valiant hero, there to rush in when you suffer. Let's be honest about what he's thinking here: he is alternately blaming you, being bitter at your -- to his mind -- cruel inattention or rejection and lusting after you. You represent something to him and he probably does not have a realistic picture of you. He is being obsessive and unstable. You will think his intentions are pure, that he is the nicest guy around but remember this: he is self-serving. He sticks with you because he knows that attrition will eventually win. It is a huge probability that he does not love you and that he simply can't find any women to distract from his attentions; they reject him and he uses you as a justification for this. He rationalises it is not that they reject him, it is that he is hung up on you so that his heart is not into it. He justifies the raft of alternate women he pursued by likening them to you (notice: they are nothing like you, except for select physical features). Stay away from a persistence man -- try to cut him off but if you cannot -- do not under any circumstances turn to him when you need someone. He will exploit this and you will regret it. Remember everything about what turns you off about him and don't let the rose-tinted glasses of friendship make you forget them: is he overemotional, clingy, strange in any way, odd-looking, abrasive, unempathetic, prone to misunderstanding or misinterpretation, overtly analytical of your actions or words, self-obsessed, excessively self-pitying, uneducated, unambitious, dependent, unfit, immature, moody, showing signs of suffering from a mental illness? Err on the side of being harsh.
He is not and will not be a friend; regardless of how friendly he pretends to be. He is poison.