Never thought that I would feel this way

Wow, I do not even know where to start. I am writing this with watery eyes because it makes me so sad, but at the same time I feel ridiculous that I haven't been able to move on from this. I am 23 and if you had told me 5 years ago when I started college that I would feel this way, I would say no way, I am not that stupid and desperate. I feel so emotionally drained, for the last year it has been difficult for me to put my energy and focus into things that really matter to me like applying to law schools and jobs. For one of the first times, I dread the holiday season because I feel so empty and hopeless, even though I have the BEST family and couple friends surrounding me and in my life. I am honestly so blessed, and feel so guilty that I feel depressed.
Before meeting my ex my freshman year of college, I was the happiest, brightest most driven individual. I worked so hard in high school to get into the top schools and earn the top scholarships. I got a full ride scholarship to my dream school in my dream city. I had an amazing roommate, met great people, studying at one of the country's top universities. A couple weeks into freshman year my ex added me on facebook, through the unversity's freshman class facebook group. I hadn't met him before, but it was pretty normal to get friend requests/ add people from the group since we were all freshman trying to get to know eachother and have fun. I checked out his fb page before meeting him and found him interesting and handsome. He was British from London, had tons of great pictures from traveling, fancy events with his family and friends. I looked on his page and there were about ten girls from the university already writing on his wall trying to initiate friendly conversations to which he replied in very charming, slightly flirtatious manners. I accepted his friend request