creepy girl obsessed with my boyfriend

Hello everyone! So basically there's this girl. Let's call her Sarah. Sarah lives over on the other side of the world and my boyfriend met her along with some other girls who he hooked up with last year on a trip before we even knew each other. The trip was 11 days. This girl Sarah was a virgin but my boyfriend took her virginity the one time they hooked up. When it was time for my boyfriend to leave, Sarah surprised him at the airport and told him she loves him. He told me he didn't know what to say or do because he only thought of her as a hookup so he said "I love you too" and left. A few months ago when we started dating Sarah started harassing me and my boyfriend and told me "he was mine! I loved him and he loved me!"  I told her to chill out and that she'll find someone else and she said okay and seemed like she was gonna stop. But now months later she's posting weird shit that's clearly about my boyfriend like "What happens between two people must remain between them. Without consulting loving relatives, friends, and girlfriends." My boyfriend claims to have no feelings towards her and he apparently blocked her on everything but it still makes me so uncomfortable!! What do I do?? ):