Why does my boyfriend get so offencive with this?

Okay so me and my boyfriend sometimes get into little arguements he's like my bestfriend litterly other than that we do everything together we take showers together ha we play video games we both wear a promise ring and were always together he basically lives with me he stopped drinking and smoking for me an he asked me the other day if he could do it this one time an I said do what you want an it started a huge argument I got so mad then later he came over and we tlked about everything an he was like I feel like you don't even want me anymore an I told him I felt the same an he was like ido I told you I wanted to be with you forever an I wasn't ever going to leave you I wanna be with you forever and I said don't promise me were gonna be together forever you don't no if you can keep a promise like that because that means a lot to me an he said of your not planning on being together forever than just leave me now.. An I was like I do but you just have to prove it an he said I will but please don't doubt it because it's not hard to be together an stay together if you can be friends with someone forever than you can easily be with me forever an I don't know he gets offencive an says if you don't think were gonna be together forever than just breakup with me now an stuff an he said if we ever broke up he would join the army or leave far away.. I don't no why he can't except that I can't take a promise he'll be with me an not hurt me I heard it all before ya no.. But I don't know what do I exspect if we really did ever break up it's changing now he barley will hangout with his friends and when I tell him he should he goes I really don't like hangingout with them I'd rather be with you your my bestfriend but right now he's with him friend playing xbox an I told him to go out an have fun earlier with his friends because tomorrow is his bday an he's spending his bday with me basically now today but he asked me of he can drink I said yeah cause it's his birthday an stuff but he's playing x box instead? I don't know but I'm happy atleast but he's not tlking to me much wich is bugging me!!