<human>: For the past year or so, one of my good friends (22M) and I have been getting a lot closer. At the start of the summer, he and I started dating and everything was going really well. We had the same relaxed attitude, similar interests, focus on fun, and it finally seemed like this was going to be a relationship that was worthwhile. I'm young, dated casually, never really put much effort into dating and just let it happen, so when this guy and I got together it was the first time I felt seriously about someone.

Summer is going by well, we're getting closer, enjoying ourselves. Things start going south in his life, unrelated to us. Basically his funding got cut for school, his job fell through, and where we live isn't exactly a prosperous area. In the same week, other friends of mine and his who had been planning all summer to move across the country have a situation fall through and they're looking for another roommate. Problem, meet solution. So obviously my boyfriend (who is the adventure type) takes up the opportunity, and decides to move north with the others. I honestly can't say I blame him for going, I would do the same in his position. We were only together a few months, so naturally we broke up when he left and we're trying to stay friends, but it is tough.

Meanwhile, an ex-boyfriend (term used loosely) from high school recently started chatting me up and I can't help myself but enjoy the attention. I feel bad because my ex, who I was / am really into but can't reasonably see myself with any time soon, only left a couple weeks ago and I know I'm just rebounding. But at the same time, this blast from the past makes me laugh, it's a great distraction, and normally I don't really see the harm in a little flirting. I'm just scared he won't see things the same way, and maybe I'm trying to justify some sketchy behaviour. Hence asking unbiased redditors like you beautiful people. What are the boundaries here? At what point am I just being a tease and am I being unfair to my summertime ex?

Could you distill the essence of the text into 1-3 sentences?
<bot>: Ex-boyfriend from the summer moved across the country couple weeks ago and an old flame is back. Trying to figure out if I'm alright to be flirty or if I'm being a tease