Op-Your dd needs to grow up, i just hope she doesn't expect you to do all the child-rearing then turn up when he is 6 and expect to have him back without so much as a thankyou.
Im sorry to say this, but your grandson will call you mum in a year or so as that is all he knows.
It sounds like you are very doting mother who has taken on your daughter's responibilies, i don't buy into that clap-trap of her being young. She got pregnant so should take responsibility and if she can't she must be prepared that her son will see you as his mum.
What if she gets pregnant again, what then are you going to be expected to bring the next child up too?, this has happened to a lady i know, her daughter got pregnant 3 times and her mum bought 2 of them up then when the kids turned 5&6 she wanted them back
, so heartbreaking for the woman that bought them up.
You are doing a wonderful thing, make it official though and adopt him as you are giving him the love and care he needs.
Tell your daughter to get some proper contraception to stop this happening again and tell her your not prepared to see her give up on another baby!
I had my pfb at 19, as soon as i saw her i loved her instantly and i would never have given up on her-you get pregnant you have to do what is best and grow up, it sounds as though in this situation it isn't going to happen especially when she can't even be arsed to buy him clothes. Atleast the father is putting effort in!
The main thing is the baby has you, and you love him so he has a stable home whilst she continues on with her childhood
Has she been checked for pnd?