How can you tell if your mate really likes you?

i have a guy friend, we have been mates for years but i don't understand him. we get on well, we'll text once in a while, and when we talk it's always about me and him, he doesnt wana talk about anything else. i once heard that he liked me but i won't believe it til i know for sure. he took me out to the zoo once, it was nice cuz he is barely free but he said he would take me out and not let me down. he's heavy on smoking and drinking and he's those type of guys you dont wana get too close to, even with girls. I always try to ask him if he likes a friend of mine cuz i wana know if what i heard was true, but he never answrs, just wonders why i always ask him that. he's a bit like me,tries to matchmake me with someone else like the way i do him. And he never stays in a relationship for too long. he's realy nice to me and wants to know everything about me cuz when i feel a slight attraction with someone, i will naturally keep my distance cuz i don't wanna ruin anythn. but yet at the same time he too keeps his distance from me, he always wants to know who i'm dating or if i'm single, and yet i know if i were to tell him i'm interested in him, he would keep a biger distance. if he realy likes me, why is he being this way? and if he doesnt like me like that, why does he give me that special attention? he even text me once saying if i ever needed him, he is there for me always. this is coming from a guy who drinks a lot and gets into lots of fights. can anyone help me out here, what do you think?