Why do I feel awful about my boyfriend lying to me on this matter?

My boyfriend and I have been through some arguments over the course of our relationship. One of them was when he did coke at a party he attended by himself. Prior to that, I didn’t know of his drug use. We talked about it and I expressed I didn’t want him to do it especially since we live long distance, are very serious and that’s not my kind of scene at all. He said he did it every week last year, and before that rarely but still have been doing it since he was 18. I asked him if he had ever had sex on drugs, and he said no abruptly in a very serious manner, said you can’t have sex on drugs, especially coke, that it is not that sort of drug. Last month we were talking about molly and I asked him if he had sex on drugs again, and he did say no again.

Last night I asked him the same question when we were discussing drug use briefly. Not sure why I did but perhaps part of me sensed he had lied. He told me he did have sex on drugs, plenty of times. Okay…

I questioned him more as I was upset about it as these were news to me. He said he used to do it 3 times a month every year, and would sleep with his ex girlfriend while on coke.

This made me incredibly upset. I couldn’t sleep. I can’t eat. I can’t stop thinking, “How could he lie to me”, and the thoughts of him coked up and sleeping with someone can’t escape my head and is making me devastated.

Why do I feel this way? Is it normal to feel this way? I tried hard to think why, so that I can maybe move on from it with peace, but can’t figure it out.