Hi April,
If an ex summer fling told me that he did not see us two being together as a possibility, and is now in a relationship with someone else, why would he now be trying to get my attention and make me jealous while he is still with her seven months later? He likes all my selfies I post, comments that I look good, and messages me late at night asking things like why we can't be friends on snapchat anymore. When we're both at the swing dancing place (where we met), he always brings his partners to where I'm dancing to get my attention.
If he was just using me like I knew he was, why would he even bother with me now if he's with someone he supposedly loves?
Thanks,
Emmy

He's trying to get your attention because he likes you! When you dated for three months and he told you he couldn't see the two of you together, it's because he sensed you wanted a serious relationship and he wasn't interested in the same thing. He was doing you a kindness by setting you free -- even though it may not have seemed that way. But that doesn't mean he doesn't like you, doesn't want to date you without a commitment, and doesn't want to amuse himself by connecting with you. He's a guy who's not ready to settle down and he's having fun. That's why he's contacting you in these various ways. He's not really doing anything wrong, and the choice is yours whether you return his attentions or not. Just be aware that he's a fun guy who's looking for fun -- not necessarily commitment. You get to be whoever you want to be, and the way you respond to him is part of who you are.