hiw can someone you havent spoke to for 2 years have such an effect on you?

ive been with my boyfriend for a year and abit... before him i was in an on/off messed up relationship with some boy i met when i was 14, at first itbwas a childish relationship but in the end we were together till we were 19. the relationship was horrible he cheated on me all the time, he messed me up so much it lead to depression. i met my current boyfriend when i was 16 and we were friends. he also knows my ex through friends. 2 nights ago i went into town with my friends, my boyfriend and ex were out together for their mutual friends birthday, this was awkward but i just thought id het on with it. my ex followed me around all night, findin any excuse to talk to me, puttin his arm round me and stood and asked me why i have deleted hik from my facebook and why if i ever see him i dojt speak.. we both agreed it was an awkward situation and i explained that it was because he treat me like shit.. he agreed. thus isbthe first time hes shown he was bothered about my new relationship.

the truth is, i liked the attention from my ex and the fact he was bothered. since then we have re added each ither on facebook and chatted thru private mail, just about everyday casual things. if this was my boyfriejd and his ex id go crazy, but i cant stop inwant to talk to my ex and i dont know why... is it just weakness of my 5 year long feelings, is it normal to feel this way when you see your first love?

i dont know what to do.