So her boyfriend is a hard core drug user that she is willingly with and you wanted her your partner? It is clear she doesn't have good judgement so.....what does that say about you? Perhaps she is emotionally vulnerable and easily influenced, does this make her good relationship material for you?
It is good that you have decided to stop pursuing her but I don't really feel your anger is warranted. Instead you might want to look at your judgement and your expectations.
Being defensive won't help you grow as poly people btw.