Bf obsessed with another girl...plz help

Sorry in advance for the length but I'm really at a loss..... My bf just cut off 1 of his female friends. He said it was bc he had a huge crush on her before we met (I knew about this) & was redeveloping serious feelings for her. When he told her how he felt before meeting me, she rejected him & he accepted she liked him only as a friend & started to move on. A few mos later he met me. She eventually moved to another state & got a bf. I never had a problem w/ their friendship. she clearly had no feelings for him & was respectful/supportive of us. The only time their friendship bothered me (& this was on his end, not hers), was a handful of times he said she was sexy/pretty/hot. He also said she was 1 of the strongest & smartest girls he knows. I asked him to stop bc talking like that about any girl would bother me but espec cuz he used to like her it was kind of disrespectful & thoughtless. 6 mos into our relationship he caught feelings for her again so cut her off. He showed me a pic of them he had hidden in a lockbox & offered to shred it in front of me. He told me once he ended their friendship it helped him fall in love w/ me even more. He said she has some qualities I'm lacking, & he told her- "its wrong to have such strong feelings for u while I have a gf." He told me she was a threat to our relationship, & she had "a strange effect" on him. On 1 hand I'm so thankful he cut her off & told her his feelings were wrong. My friend said that shows how much he loves me bc as much as he cared for her, he was willing to kick her out of his life to make things work w/ me....but idk. If he loves me then how could he develop such strong feelings for another girl? I'm so hurt by him falling for someone else while were together. & it made me feel like complete c**p that he fell more in love w/ me once she was gone. It's like he cared for her more & I fell in the shadows while she was in his life. i feel 2nd best, like he settled bc she didn't want him. Would u dump him if u were in my shoes?