Why does she act differently towards me now?

This girl Iv liked for three years is suddenly acting nice and sweet around me. Iv noticed that she hasn't mentioned her bf in three months and that exactly how long she started acting different around me. Iv also noticed that Everytime I ask her out on a date she says aww and she starts to smile but she says she works alot and she won't have the time. Before when I asked her out she would just say she was busy and that's when she was in a relationship but now she actually considered spending time with me and she actually gives me a more sincere answer than before I give her a hug and a kiss on the cheek Everytime I see her and when I kiss her she always looks at me and smiles. Finally what also was strange is that she feels really uncomfortable showing any type of skin when I'm around like she would ask me to look away if she had to fix her bra or her shirt etc she literally feels awkward when her bra is showing in front of me but today she had no problem showing me her bra strap and she was showing more cleavage when I'm around. She and I always were physically attracted to each other but nothing ever happens between us.