Since Vim cannot guess your thoughts (yet), you have to tell it explicitly when a new line does not continue a multi-line comment.
A straightforward solution is to simply delete the autoinserted comment leader with CtrlU in insert mode. See :h i_CTRL-U
.
This key combo also works in most terminals, by the way.
In case you don't like autoinserted comment leaders at all, you can disable them with the command :set fo-=ro
. See :h 'formatoptions'
.