Just because we aren't official is it okay for him to be flirting with other girls?

So my best friend told me that he really likes me, and likewise I really like him too. However, he's in England right now and I'm in Canada.. So he claims he has insecurities due to his previous relationship, and doesn't want to ruin our friendship at the moment. Despite him saying that, he talks about us getting married, calls me all the time, tells me I'm beautiful and what not. At the same time, I see him flirting with other girls on Facebook and stuff. I mean yeah, we aren't committed or anything.. So he can anything he wants. But really after telling me he likes me, should he really still be flirting around?