How to not Fall into the 'friend' zone with him??

So im gona cut my story short.. Pretty much I’ve known this guy since like I was 16 & we were talking before but drifted away with uni and stuff. fast forward 2 years later or so .. I have changed a lot! and so I guess he took notice and we randomly started talking here and there again (over msn) just recently I bumped into him after 2 years at an event .. & even though the msn talking was there, we both were in a bit of a daze to see eachother.

I made it quick like just a hye and hows it going. however when I was chilling with my girlfriend I saw him still staring at me. I pretended I didnt notice. then when he came back fromt he event ..he msgs me saying how he was sorry about not being able to talk but he wanted to sit and talk with me & he complimented me as well. (which isnt him cause I’ve always known him to be reserved) .. we ve been talking more frequently since ..but its not been long at all. I had one convo with him where he was a total clown..it was like I was seeing a diff side to him and just like 2 nites ago we had like a long intense convo but it was more like friends ..but about issues were both passionate about. and somewhere in the middle he paused again and said jeez I wish I sat with you andjust talked to you there. But towards the end ..his goodbye was casual and he called me dude! lol :(

Anyway.. I dont wanna fall intot he friend zone with him. How do I prevent that from happening?.. im not gona ask him out or anything since were just getting back into talking after like 2 years. and do you think theres a possibility that hes interested in more than just friends? hes complimented me quite a bit on how I am as a person. I’ve been told guys take their time pursuing a girl and are more laid back. Is he just being friendly or is he trying to establish a friendship to see if anything can come of it..hes been opening up a lot bout his opinions and thoughts and also about the little things he wants to do.

HELP!lol