The chemicals we release in our brains when we become 'attracted' to someone have be proven to be addictive (Leil Lowndes discusses this in one of her books). I can't remember the exact science as she explains it but that's the upshot.
It sounds like you're 'protecting' yourself (from all the potentially negative emotions love can bring:rejection, heartbreak, insecurity etc) by only allowing yourself to fall for men who are emotionally and ,in this case, literally unavailable.
I'm guessing you usually go for the 'bad boys' and have been through at least one quite serious break up which has left you unable to allow yourself to fall in love with anybody else since.
Not trusting people, making yourself emotionally unavailable, and keeping people out of your life for the wrong reasons is nothing more than a defense mechanism, there's a cost and a benefit to everything in life, by doing this you're not even putting yourself in contention for any of the benefits that loving someone can bring you. You need to accept that by learning to trust and love someone you HAVE to hand over to them a degree of responsibility and control (not too much or you become co-dependent, too little and the 'bond' will never really be created) which they have for your happiness and emotional well being.
Relationships, like life, are a contact sport - players get injured, they score own goals, they make epic wins and suffer ego crushing defeats - don't force yourself into early retirement for a minor injury.
Imagine you're a millionaire (if you're in the fortunate position of not having to imagine then billionaire) and one day you get burgled, and lose some of your money and possessions, so to protect yourself from further loss, and to prevent such an injustice ever occurring again - even though you can afford to swallow the loss and know you'll make the money back - you decide to react irrationally and you sell everything, and put all your money in the bank so they can protect it and keep it safe, the only problem now is that nobody can enjoy it or share any part of it any more. Despite its existence it's totally unavailable now to anyone, even you. So take some money out and start spending and enjoying it x