Feel very sad

There was a girl I developed feelings for. I thought she liked me as well. I went out to a bar in a group she was with us and the entire night her and this tall guy were so into each other I literally heard her say "he's like a human shield" and she kept leaning on him and hugging him and all of a sudden I was just invisble no one And i just felt really sad..I really thought we had some connection But nothing They probably had sex I left the bar really sad