Relationship help don't know what to do?

I recently started a part time job and this lad added me on facebook, started texting and bit flirty, and the next day we met up, i just started there a spoke about things which i had never told anyone before and we hugged and kissed. then we met up again and the same things happened. I cant stop thinking about him and because im on till at working im always facing him i cant stop looking or smiling at hm. i told him i liked he but the thing is he has a girlfriend but she away and she comes back soon and he said never know what might happen. i really dint know what to do i really do like him and he leaving work soon to start a new job. he says im amazing and how differnt i am and he says im pretty and that but i dont know what the hell to do help.