Lovesick Over Some1 That Left Me 4 Another Girl After 3 And 1/2 Yrs Together

I've honestly never done this before. But I'm so depressed and lovesick idk what to do anymore. I had been with this guy for 3 1/2 yrs and everything was perfect until he told me out of nowhere he was going to join the military. He just blurted it out and I got really upset and exploded on him b/c I was thinking to myself after 3 1/2 yrs how could you just blurt out something like that without even asking for my opinion knowing how much it was going toeffect our relationship. I was so angry b/c he just said he was going to go whether I liked it or not so I broke up with him/ that night. In the morning I regretted breaking up and said we could work it out if we both tried. He completey cut me off and said no you said we're over. I cried and texted him and called him literally 50 xs a day. The first week he just ignored me. The 2nd week it soundedl like he missed me b/c he started calling and texting me like he used to. But everytime I mentioned of us getting back together he would literally ignore the ? or say he had to think about it. He said it was my fault for slacking off on our relationship plus that he was having a lot of problems.This went on for 2 weeks. I hadn't checked his twitter in a while so i went to his account. It turns out that in those 2 weeks he had been talking to, going on dates, with this girl he just met. I was completely heart broken. All his tweets were about love and that girl. I just thought to myself how is that after 3 1/2 yrs he didnt even follow me, post a pik, or even tweet about me yet this girl he just met he's tweeting nonstop about her and to her. I just don't understand how after 3 1/2 yrs he throw all our memories away and played me. In those 2 weeks he kept my hopes up saying he just needed to think about things first before we got back together yet there he was wit another girl that whole time. I don't understand why he did something so hurtful 2 me. If he just didn't want to be wit me why didnt he just say so instead of making up an excuse that he was going to go to the military and that he was having a lot of problems. I just don't understand how he went from 1 day saying te amo to the next day with another girl. I told him in those 2 weeks i would take a bullet for him any day. Yet there he was wt a girl i didnt even know about. Im in such pain right now I havent slept in dayz, i've lost 8 pounds, I can't concentrate I just don't know how Ima get over this.