Did I fall in love with a skank?

I met a girl, fell in love, treated her like absolute gold, never lied to her, her family loved me, we had full intentions of getting married, and then she started a new job, got in with the wrong crowd, got into drugs and cheated on me with her dug dealer, now I always knew she had a not so great past with parents and other men, but she said she found what she was looking for with me, now she "found what she is looking for" with this guy, did I just believe all her lies? Is she really just a skanky loser girl that cheats on every guy she's with?