You're falling for Richard III.

It seems as though quite often someone is dating a great guy, a nice, sweet guy, but that's just the problem, "He's too nice."  We don't know why but we all want the evil one. We want Richard. Here's Why:

I think the most dominating characteristics that makes a villain a villain is their ability to manipulate, and we see this within the character of  Richard lll towards the play characters and the audience.  

In the very first scene of Act 1, Richard goes on his tirade about his villainous ways stemming from his traumatizing life lacking love and suffering from a daunting physical deformity.  While he speaks of this, the audience is drawn into believing the other characters in the play are the evil ones for ridiculing his helpless appearance, and that we ought to sympathize with Richard despite his thoughts and actions.

We also see Richard possessing a complicated and intricate mind full of self-reflection and intellect. It is the "brains" that often make a villain as menacing as he/she seems to be. Have we ever seen a truly evil villain who is foolish, and simple minded? The Joker in Batman may be as evil and chilling as he seems because of his unparalleled thoughts and theories and plans. They would have no success without their 'brains," which also correlates directly to the unnerving ability to manipulate. 

Richard's  foolhardiness and perseverance lead him to not stop at anything to achieve his schemes, and his mental state of pure wickedness allow him to disregard the normal moral and ethical dilemmas a non-villainous person would adhere to.

So his villainous traits lead him to both manipulate and also impress us, so it is this awe and sympathy that blind us from his real nature. And it's not just the audience that falls victim to this. Lady Anne, who knows very much of Richard's true self and true motives and desires, still somehow allows herself to fall into his seduction. He relentlessness and intelligent wit with words plays into this. 

It is not until the end that we can fall out of his trance to see how evil he really is, as his nature becomes explicitly apparent. So after he charms your parents when you bring him home, and after countless dates, you'll realize you should have never left that guy who was just too nice...