One thing i can forsee is someone's feelings are going to be hurt between the 3 of you. Its important to note that because you and this other guy are in a race to get her you seriously need to consider your position. Part of why you are so compelled to be with her is because of the past. I bring this up because right now you have no true vulnerability attached to the girl other than your history. Its important because considering the situation if you do win her over you will still have to deal with this guy regardless of the baby because she is now tied to the baby and the father. Im sure you thought of this already but its actually quite difficult to comprehend because chances are you are head over heels for this chick.
Obviously the choice is yours here. Decide wisely.
I got to thinking more about her position and im starting to wonder if she's only latching to you for emotional support. Are you ok with being friend zoned? Chances are high if she's going to try to make things work out with this guy if shes having the baby. Even if you havent confronted her yet about what she's looking for with you in terms of frienship or lover / step-father to her child you have to consider your feelings when events reveal themselves because to some degree its really not unexpected that she would still seek to create a beautiful relationship with this guy up to and after the baby is born.
You said she isnt in love with him. Sure that might be believable but do you know if she hates him? If she broke it off with him? Or vice versa? You might still want her but what if she doesnt want you? Consider than last night her talking to you was not with intentions to hook up and rekindle. Consider the option that she is looking for emotional support because she isnt getting any. There is a possibility that your likely to be friend zoned just because of the variables. In the coming months her emotional radar will flip flop if she decides to keep the baby.
I'm telling you this as a cautionary tale because its no longer just dating or getting back together. You're considering jumping through life hoops to be with her. Will the reasons why she originally broke up with you even mend? Did she give you a reason? I keep askin these things not because you havent asked them yourself but because sometimes hearing someone else tell you what you might have asked can help you commit more to your decision or walk away. For an excersize even consider her saying this stuff to you. You need to be ready if you're going all in... Good luck