On a side note maybe if you wish to stay with her and value her as you say you do, not to sound like I dont believe you but honestly I dont know you so your word is all I have. Maybe think about what you are really sad about obviously there is a sense of loss because you are losing this ideal you had in your head for all your life and possibly theres a sense of loss because you feel like you will miss out on the whole pregnancy experience with her. But is what you would give up really worth the experiences you would gain if you had a baby with a different girlfriend down the line instead? The way I see it it kind of seems what you are losing is not that much considering the child will still be brought up by bith of you and I think she will love the child and be grateful just to have the chance to raise one. That being said remeber that she is going through grief in this too because she lost something she probably hoped she would get to have, which is a baby of her own and going through having that baby grow inside you for 9 months and developing that pregnancy bond with the baby but that doesnt weigh in a fraction into the time and effort spent to raise a child and love them so I would not weigh it too heavily but consider going through the grief first before making a choice that will weigh this much.