Relationships

Why would she behave like this?

I was with my boyfriend for a year when we had to long distance for 6 months due to studying. After 2 months I visited him and all was good. 2 weeks later I saw a girl liking all his photos so I texted her and asked her to stop liking his photos. She texted back and said that he was her love. I replied 4 times asking for proof and evidence. She start asking questions about our relationship and I answered her but she would never respond when i asked her for proof and evidence. I sent her a picture of me and him together and asked her again to send me proof that he was her "love"and she still didn't. I texted her and asked her to leave him alone and she saw my message and did not text back. My boyfriend said he knew her from mutual friends but nothing ever happened with them. My boy has always been faithful also.3 months later I rang her by accident and she responded rudely and then start saying how her and my boyfriend went to a hotel together back In January in the city. I asked more qs and then she blocked me. She also sent me the pic that I already sent her of me and him 3 months previously. My boyfriend was very angry and said she was crazy and trying to break us up. A few weeks later I told her to stop spreading rumors and she sent an audio message saying they went to a hotel in January and that was that. Then a month alter she texted me again and changed her story and said that they actually went to a b&b downtown every Saturday in the months of December and November and she never said anything about going in January. I looked up the b&b she named and it only opened in April and she claimed to be there in December and before. Meanwhile, my boyf is denying all of this. I texted the girl about changing her story and the b&b not existing and she went absolutely mental down the phone and called me all kinds of names and then blocked me. Whats her motive here?
Why would she behave like this?
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