Puck. Then will two at once woo one; 1155
That must needs be sport alone;
And those things do best please me
That befal preposterously. (Shakespeare 3.2. 1154-1158)
This shows how Oberon is telling Puck to put love potion on Demetrius’ eyes and for him to not wake him from sleep. It also shows puck thinking about how lysander and Demetrius will compete for the same girl which shows that he has put the potion on Demetrius. This quote supports the thesis because since Demetrius was bewitched into love with Helena. That proves the only way he will stop loving Helena is if the love potion is removed and under the circumstances that only one fairy can do that it is unlikely that he will end the relationship with Helena.
Another example to show how Demetrius and Helena will be the most successful couple is the fact that Helena loves Demetrius so much that she will do whatever it takes to be with him. Helena is pursuing Demetrius through the forests trying to persuade him to love her. When she catches up to him she says,
And even for that do I love you the more.
I am your spaniel; and, Demetrius,
The more you beat me, I will fawn on you:
Use me but as your spaniel, spurn me, strike