Normally it you have to connect two Tamagotchis many times in order for their relationship to advance to the stage where they're in love with each other. A Tamagotchi character who has just recently consumed the love potion will immediately fall in love with which ever Tamagotchi it is connecting to, even if it's never connected to it before. Note: the effects of the love potion only work on the one who consumed it.
Example 1.
Tamagotchi A consumed the love potion. Tamagotchi B didn't.
After they connect, A loves B, but B doesn't love A.
These Tamagotchis can not yet mate.
Example 2.
Tamagotchi A consumed the love potion. Tamagotchi B also consumed the love potion.
After they connect, A loves B, and B loves A.
These Tamagotchis can mate immediately.