@EggHead,
There's nothing about your reaction with which I would take issue.
If you are in a serious relationship with a woman you have every right to be displeased if she invites her ex-husband to live in her house despite your reservations.
Relationships are a two-way street. There is no requirement that you suppress all of your feelings and concerns and just go along with what she does or wants to do. It not about being controlling its about being considerate.
I'm assuming it's a serious relationship based on what you've written and in serious relationships both people take into consideration the feelings of the others.
I don't think you are at all being unreasonable. Yeah, it could be argued that your concern indicates that you don't trust her enough, but the same argument could be made if my wife expressed her displeasure with me staying in the same hotel room with a female employee. If she truly, truly trusted me, what would the big deal be? Of course that's nonsense as would be any assertion that you don't trust your girl-friend enough.
Although you don't seem to have indicated it is the case, your concern could be that the man who abused her before could abuse her again.
No matter what the source of your concern, your girlfriend should respect it.
As you've noted you're not trying to let your personal feelings get in the way of her caring for her daughter. It does stretch credulity that there is a significant enough difference in the measure of benefit to the daughter between her father living near by and being allowed to frequently come see her and living with her in the same house. And whatever that difference is, is it worth, upsetting you, and ending a relationship which is supposed to involve her loving you?
Obviously she thinks it is which either means she has a very strange conception of the the value of the man being her daughter's father or she just doesn't care all that much about your relationship.
If you were demanding that she never allow the guy into her house, it would be a different story, but you're not.
I can't know what's going on in her head, but I think you're perfectly justified in ending the relationship.