What is his deal? is it my fault or is he just immature?

So the other night we had my birthday party and my extremely attractive neighbor that lives behind me and i ended up making out the whole night. We were both kind of drunk but i went back with him to his place and we messed around. I don't exactly remember how it came about but i just know i told him that i just couldnt sleep with him. (it was the first time we had ever actually hung out & he lives right behind me!) It was a really good night and last night i text him to ask him if i had left my jacket there. Anyways we started texting and he implied that he was interested in my cousin who was at my party too. She lives about 5 hours away in another state and she is moving down to live with me in the summer. He asked if i would initiate the whole thing because he really wanted to talk to her. I thought it about for a few minutes and if he is going to try and sleep with me and then want to talk to my cousin & not me then he is not for me. So i informed her that he told me that 'he was going to marry her' (those were his words) and she said to give him her number. So i did. I text him earlier and he said that they text a little last night and that was it and then we text for a little after that. I am a very conflict avoiding person & i do not like drama so i was trying to not be a ***** although he really pissed me off because how he was with me the other night. He initiated the whole making out thing. He is about to be 20 and i am 22. My whole question is what was his deal? did he think i was drunk and easy? My cousin was around for all of a little over an our and she has no clue that any of that even happened between us. I mean before he told me that about wanting to talk i actually had a crush on him. Is he just young and immature? or does he not like me bc i didnt sleep with him? or would he have probably still been interested in her anyways?