I also agree that getting married just so that i can become the childs legal father is not a good idea. Thats why i wanted to do it without doing so but from what i can see that is really the only way or me to accomplish it. ( so once again that is why i came to this forum before doing anything at all, and so that i would have a much better legal understanding of why or why not it would work or be a good idea to go through with this action). But i really do appreciate all the legal and " moral" advice that i have been given here.
Legally:
1. You will almost certainly not be able to adopt if you're not married to Mom.
2. Adoption creates rights AND obligations. If you and Mom divorce later (which is quite likely), you could get custody and Mom end up paying child support. Or Mom could get custody and you would end up paying child support for years.
3. If Dad has not been established legally as father, then the whole exercise is moot - he has no rights anyway.
Now, in a non-legal sense:
You are apparently operating under the misguided belief that being a legal father enables you to be a better caretaker and model for the child. That is not true. Without adopting the child, you can be the best model in the world (assuming that you have Mom's permission, of course). You can love her. You can tuck her in at night and read her bedtime stories. You can take her camping. You can take her to DisneyWorld. You can teach her to ride a bike. You can be there when she falls off her bike and scrapes her knee. She can call you 'Uncle Eddy' or anything else (except "dad" or some derivative thereof).
There is only one thing you gain. If something happens to Mom, you would be able to keep the child. But the risks of that are pretty low since you're apparently young.
Of course, on the other side is that if you were to marry solely so you could adopt, you would be sending all sorts of messages to the child - about how marriage is about convenience and that it's OK to marry someone for the wrong reasons.