I have been secretly adding soylent to my girlfriend's husband's shakes
Why would you add an ingredient like this to the shakes?
I really want her to leave her husband.
Firstly, you shouldn't even be seeing this woman since she's married. Secondly, you should not add stuff to people's food without the knowing. Break things off with her since it sounds like she's not leaving her husband for you full-time.
I'm going to mix in cinnamon, and a lot of it!
Why do you continue to mess with these people's foods? You already are involved in cheating since your girlfriend has a husband, so why make things worse and mess with the husband as well. You are really messing with this husband's emotions big time here.