He came in me and I told him not to

I got pregnant last year at 15 and it ended in a miscarriage. I didn't want to be pregnant but at he same time, my boyfriend and I were both very sad that it ended that way. We were sitting down at his house the other day and he brought up the miscarriage and how it still makes him sad and he wonders what it would be like if I did have our baby. I recently made the decision to tell him not to finish in me anymore due to fear of getting pregnant again. (I'm on birth control but recently thought that I don't want to take the chance anymore since I'm still only 16 and he's just now 18). We were having sex and I told him to pull out... he didn't. I asked him why and he said he had baby fever. I didn't even think guys that age want a baby!! So, we decided to get a puppy. Two weeks after having him, he still talks about having a baby and how I would "be a wonderful mother" and how he wants so badly to be a dad. I don't know where all of this came from and why he wants to have a baby at this age. It's making me feel crazy because part of me is starting to get baby fever while the other part of me is asking wtf I'm doing.

Do any of you have any idea why a guy this young would want a baby and why it's just coming up now? All opinions welcome