Need to vent and a perspective

Last night I found out for the first time that my boyfriend of 7 months smokes e-cigarettes. He knows that I am totally against smoking because my dad died (at 34) when I was 5 due to smoking. I asked him to reconsider quitting it but he said he does it because he wants to do it. After research, I know that they aren't as bad as smoking cigarettes, but I just hate it and don't want him to do it.