The Guilt Is Unbearable

I have been with my boyfriend for almost 4 years now. For the past couple of months it almost seems like the emotional aspect of our relationship is lacking. Instead of talking about it, I continued to let it be that way for multiple months. I go out seeking attention in the wrong places and continued to let my relationship slip out of my finger tips. I have NEVER cheated on my boyfriend over the past four years but last night I made the biggest mistake of my life. I was very intoxicated and slept with someone I knew nothing about and it was absolutely meaningless. After this occurring I realized that I made a huge mistake and realized I do truly want to fix things with my boyfriend and I need to regather myself and become an all around better person. My boyfriend always tells me if I cheat on him, he’ll leave me so it was very hard to see and look at him in the eyes the next day after knowing what I’ve done. I don’t want to tell him because I know it’ll just crush him and he’ll step out of my life, but instead I feel like I need to learn from this and never do it again. But the guilt has been making It hard for me to eat or be happy. I don’t know what to do but know I don’t want to lose him…any advice would help.