Letting go of a step daughter

If you were in a relationship with a someone who had a child before you got together and you break up afterwards, do you let go of the child too? Considering you are close to the child and take her as your own. The child is also under three years so she is not able to make decisions on her own.

This is a situation I've thought of many time (however, in the reverse.) It's not an easy thing to handle by any means if you're especially losing a daughter without a say in the matter. Ultimately, I would say let it go. The decision, unfortunately, is up to the other parent. Continuing the relationship (in the long run) may cause more harm than good. Such as the other person moving on, a co-parent (if applicable) having issues with it, mixed signals to the child, etc. I have never been down this road before so I may be wrong.
Best of luck

This would be such a heartache. I can only give a guess because I've not been in the situation and the people I know who had to go through it all let the kids go. when the relationship ended.

My gut instinct tells me that since you don't have any legal rights where the child is concerned, the only way to continue to see her or be in her life is if her dad (and mother if she's in the picture) would allow it... and I'm thinking that doesn't happen very often.

It also needs to be said (don't throw things at me!) that you'd have to be sure that it wouldn't be with the purpose of keeping her dad in your life before you bring it up to him that you'd like to continue being in her life. I truly know a few people who would do exactly that and use the child as a way to get back together. I'm sure you wouldn't, but I throw it out there when I think of something.

There has to be mutual agreement between you and the child's parent. If you both support you raising the child with some support, then it will be reasonable; but the child's parent cannot walk away from the responsibility that is not fully yours.
But you must be willing to let go if the breakup would mean you would not be responsible for the child anymore.