Why do we ignore all imperfections in people we fall in love with for a couple of months, but after a certain period we start noticing imperfections?
Can hormones - or any chemical - be used to influence someone to fall in love with you?
Yes. The chemical/hormone that causes attraction is called serotonin. That's what causes attraction between two people. Theoretically, chemicals can be used to make people fall in love with you, such as MDMA, which increases serotonin levels. If the "animal" (such as a cat or a monkey), was in the same room as you and you gave the cat MDMA and you were the only one in the room, the cat would bind with you and seratonin would be released.
This is why MDMA and methamphetamine are known to cause homosexuality and fetishism, for the drug tricks the human into thinking that serotonin is formed with a guy who he is hanging out with or what he is doing at the very moment.
Another hormone that is a "love" hormone is called oxytocin, but this chemical will only cause bonding once the love is formed.
In short, serotonin makes someone fall in love with you, while oxytocin will keep someone in love with you.