annoying isn't it? a clingy ex.  
Try to trust your bf.  after all the key word for her is "ex".
He is with you by choice.
Try laughing at her behaviour instead.
hugs to you, and lots of positive vibes.

Dear trust your partner and don't give her power, the more you ignore, the faster she will get bored... While she is still around laugh at her ridiculous behaviour.

I wish lots of happiness! BIG hug!

SHe blew it and it is over between thwem. It sounds like she knows she lost a good thing. So writing her an email and telling her to keep her hands off of your bf is like putting the red flag in front of the bull.

If you let her know you are concerned about "their" past relationship and her attempts to "get him interested again" will make her think she is getting to you.....she will continue.

If she succeeds in throwing you off balance emotionally, you may have the tendency to react unwisely to circumstances she is attempting to create, rather than simply responding to her desperate actions with conscious intelligence.

Concentrate on creating the quality of your relationship with your bf and sincerely bless his ex for loosing and greiving what you now have. Be compassionate and generous of nature.

Let HER actions be the re-enforcing reason why he stays away from her.

It is about maintaining the beauty of the connection between the two of you, in the present. With the qualities present in your relationship, he will be more inclined to keep past relationships, in the past.

hugs to you

i agree with what every one has said and hope things get better for you heres a big hug to you and positive energy