Feeling so empty and lost! Just lost my 1st love after 11 years :(?

Dunno what happened it just happened out of nowhere...I'm 28 shes 27 and weve been together since i was 17 yrs old....I proposed to her 3 yrs ago and was committed to this girl..I NEVER cheated on her in the whole duration into this relationship...4 yrs ago she cheated on me with her friend...i took her back and everything was fine and a yr later she left me and come to find out shes with the guy she cheated on me...6 excrusinating months goes by and we get back together..EVERYTHING was picture perfect for the 3 yrs..she didnt go out as much and seemed more serious about us...she even told me she wanted to get married and everything...I had no doubts or worries about us whatsoever...but the past 2 months i've been getting a weird gut feeling like something was up..the sex drifted away..and she wouldnt give me any attention..well this feeling raised my curiousity level and i snooped through her phone and found a recent picture of her and the guy she cheated on me..i couldnt believe what i saw..my heart dropped..her explanation was she was drunk so why not and who cares that she didnt do anything with him..I told her she needs to stay away from him blah blah blah...2 weeks later my buddy texts me and tells me he saw her at bar dancing near him and talking to him..her explanation..i talk to everyone...then this past monday my friend texts me and says dude we need to talk in person..so we meet up to local bar and he tells me that saturday he saw her and her friend hang with this guy all night....and all 3 of them left together...she said that he was just walking them to the car since they were drunk..and granted that night she didnt come home....(she said she stayed with her friend) i know u guys are sitting here and saying WTF is this guys problem LEAVE HER..but I LOVE THIS GIRL SO MUCH and when i sit next to her and look at her I DONT SEE THIS girl that would do this...she tells me that I always look depressed and this and that...ive been being depressed lately because of all this **** and how she doesnt even give me any attenton...b4 i got that gut feeling i was PERFECTLY fine...I asked her the other day...WHY DO U HANG OUT WITH HIM..i deserve the truth and the only thing she said was..."forgetting about this guy what was wrong w our relationship" she wouldnt answer the question i asked her...now shes acting like she dont give a ****...THIS IS SOO TOUGH ON ME!!!!!!!! WHY DO I LOVE THIS GIRL SO MUCH...I COME HOME TODAY AND SHE WAS HOME AND SHE SAID SHE was tired and may not go out tonight..i tell her why dont u stay home and watch a movie that i rented..she says well im going to try to go out..so she slaps a sexy black dress and says have a good night and leaves!!! And i'm a good looking guy people say i can get anyone i want..I even went out yest and lots of girls gave me attention..but I have no desire for any other girl..someone please show me the light Im going crazy!!!!!!!!!!!!!