I hurt myself and lied to my boyfriend about it. Should I tell him the truth?

my boyfriend and i have been dating for 7 months. I haven't hurt myself in almost 2 years. but last night we got into a bad 'one sided' argument, it was all my fault but I was still mad because I have trouble admitting I was wrong and blahblah blah. I was super upset and sad and he just fell asleep. then I started to think about how shitty of a girlfriend i am and how if anyone makes the relationship unhealthy it's me, and then I started thinking about how much weight I've gained and all that shit. so I went and hurt myself on my arm and leg. he saw my arm and asked me what happened and i lied and said i didnt know. I've never lied to him before and I feel horrible about it, but we were talking about our fight last night and he was crying and had to go to work soon so I didn't want him to feel worse, or go home and hurt himself as well. what? I should i do? I feel horrible for lying but I don't want him to feel worse, and like it was his fault