Everyone is drawn to that special type of energy. When we find that special type of vibe with someone we have a conversation with effortlessly, someone we click with and have deep conversations with and talk to all day about nothing, the gravity pulls in. Without resistance, we give into that magnetic pull and believe what they tell us. What they tell us is what we wanna here, how they treat us is how we've always wanted to be treated, the feelings they share has to be sincere. Someone is finally giving us what we finessed since we were little. 
As humans, we're naive by nature and lash unto the idea that everyone is good and has our best interest. But that leads to disappointment, it leads to heartbreak, it leads to asking ourselves silly questions like "how would I have been so stupid", " why would I have believed the lies they fed mhe"? 
But Its never you're fault. There are so many people out there that take advantage of people and manipulate their emotions without any feeling of remorse. Don't allow them turn you cold, do not allow them make you not trust anyone anymore, do not allow them ruin love for you permanently. Take the lessons you learn from them and be a little more patient when you find someone else, take a little more time to develop trust for people, take a little longer to fall in love. Give people the opportunity to show you their true colors before you give an opinion of who they are and what they're capable of, give people time to show their true character. 