Why did he suddenly loose interest?

So me and my new crush never met in person and met online through instagram , both newly single after TWO year relationships. I don't know what his side of the story is but judging from his photos he was really inlove with his ex and might still be, since he still likes every photo she posts and they broke up recently on NYE. However he NEVER mentions her to me. Its been 2 weeks of texting and he finally asks me out. We had decided to go out for dinner on Monday but everything got ruined when we accidentally met at a party on Saturday. It wasn't akwurd or anything but he was really tipsy and not nervous at all to see me in person. He was too friendly and touchy for a first meeting. We danced laughed and he ended up kissing/biting my neck and nibbling my ear. He didn't try to kiss me at all on the lips even though we were really close and the tension was heated between us. When I left he called twice asking if i was home and if i had fun. We even talked later that night till early morning about what we liked or disliked about each other. He said he liked me a lot and was excited for the dinner on Monday. He even chose the place and everything. But the next day (sunday) he said goodmorningg and I replied but he didn't go further with the convo. I sent him a cute photo of my dog two hours later but he didn't answer even though he read my message and was online often. We didn't talk at all after that and tomorrows Monday. What happened to the guy from yesterday?
Why did he suddenly loose interest?
Add Opinion