It sounds to me like there are a couple of issues going on here. First off, it's sounds like you're bored in your current relationship and you are "confused" because you miss that fun spontaneous feeling you had with the other guy, but at the same time you feel guilty for having those feelings because you are with a guy who's essentially done nothing wrong.
What a lot of people don't realize is that those spontaneous feelings and instant attraction rarely last. And, you cannot build a solid relationship off of those feelings. What usually happens is that when those feelings fade, you find yourself longing for them to return, and you find yourself feeling like you should "love" the person you're with even MORE after all the time you've been together.
As I've said, these lusty, fun, and dangerous feelings rarely last and are almost always replaced by a deeper feeling of true love once you've found the right person. If your feelings have diminished for your current boyfriend, then it's time to move on. You obviously don't feel that deeper attraction that is needed to sustain a long HEALTHY relationship with him. Staying with him out of quilt or obligation in your own mind will only lead to your futher unhappiness with him. Some people just don't fit. You don't have to be in BAD relationship to realize you're with the wrong person.
But is Mr. Dangerous any good for you either? Probably not. The reason for this brings me to my second thought. From reading your post, it sounds to me like you tend to jump from one relationship to another with no break in between. (this is just what I get from your post...) Let me explain...first you get with this guy while you're still with your boyfriend, then you move in with him, then you break up with him, then you move back in with your current boyfriend, buy a house, and now you're having feelings of getting back together with Mr. Dangerous.
Relationship jumping is a bad thing. I don't know how old you are, or where you are in life, so let me use myself as an example. I used to go from one girl to another...always making sure my hand was securely wrapped around one vine before letting go of the other (just in case it didn't work out with the new vine...I could keep swinging from the first one). I would go from "serious" relationship to serious relationship, never finding what I want...always comparing the new vine to the old one.
And I would swing from one vine to the next as soon as that hot lusty fun feeling would ebb. "Ah...SHE'S not the one either! Why can't I find the ONE?"
Then one day, after letting go of the old vine and missing the new vine, a friend of mine told me something that I discovered to be quite true.
"If you cannot be secure and happy by yourself, you will never be satisfied with anyone you are with."
You seem to have the same problem I did. You don't know WHAT you're looking for...but you're searching. But before you can seek Mr. Right, you have to define what Mr. Right should be. How can find what you don't know you're looking for? The best way is to do this...
Take some time off. Break it off with BOTH. Don't let old feelings get in the way of new adventures. Then, step back and find YOURSELF. Find out what YOU want and how you want to get it. Then define the man that best FITS into your life's plan without you having to alter either your plans or the guy. Then go find the man who fits that criteria.
Then, armed with this new insight and a clear direction, go out and date as many guys as you can....don't move in with them...don't get serious...
Only by sifting through the straw will you find your needle.
I hope this makes sense...my needle is telling me I have to hurry up so we can leave!!! I had to cut this a bit short!