I agree, you have far bigger concerns right now, that one's a long way off. It's good to be thinking about it, but you don't know what your life will look like in a few years when the issue actually comes up. Unless the mother completely leaves, which I'd be very concerned about, your child will know that she has two mothers, and you can bring up which one gave birth to her. Point out what physical traits she got from her, talk about when she was in that mommy's tummy, etc.
You definitely want to make sure that you're certain things are going to go as planned, and prepare yourself if they don't. You may have had an open relationship, but especially if you cheated on your girlfriend, you do want to be sure that your girlfriend will raise your child and give her the love she deserves- especially if she'll be the primary mother figure. Also, why is the mother giving you primary custody and apparently wouldn't be very present in her child's life? Unless the woman is likely to be abusive or negligent, it's in your child's best interests to have all parents in her life.
(also, just in case you don't know, it's possible for your girlfriend to induce lactation so the baby can be breastfed even if not with her gestational mother. If she doesn't want to do that and you have any questions about formula, let me know.)
this is just a moment in time, step aside and let it happen
Last edited by sillysapling; 06-18-2014 at 04:47 AM.