Why did she leave me for her ex?

yesterday I saw one message where she written i love you I love you soooooo much I love you infinity and said you are mine and I am yours and after one month she leaved me for his ex and said that she never loved me she only came relationship with me for forgetting his ex and this line broken me but after this also I never left her I said okk let's start from new and told her to tell your friends about me and after this she blocked me I tried 300 calls after getting blocked but she not respondand yes I loved her so much but I know she never loved me after being relationship with me for 1.5 years and that's okk it's 34 days of no contact and I don't have any friends and I managing alone by myself