Why is she doing this?

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I met this girl last summer and we have hung out a couple times while we've been home from college since then and we get along pretty well. Lots of flirting and joking around with each other. Throughout the year we have communicated every couple days be it via text, or Snapchat. She frequently like my photos on Instagram and Facebook, and I do likewise. We have never kissed or anything, but when we were both home for our towns St. Patrick's Day parade, we came very close, but she was a little drunk and I didn't want to appear to be taking advantage her, and our friends were with us and I'm a little shy and didn't want to kiss her in front of our friends. What confuses me is that today, after not talking over the weekend, despite the fact that we were both home for Easter, we didn't see each other, she sent me a Snapchat of her and in the background, there is a guy who she circled the face of with a red heart. He is lying on a bed and she is sitting up, they are both fully clothed, but it irks me... Granted she goes to a school that is 85% male (its a military school) I think he might just be a friend and she may have done it just to rile me up a bit. What are your thoughts? Please help, thanks!