I'm baffled

My boyfriend and I have not been in a good place since his daughter was born. It was bs after bs but we kept dealing with each other simply out of the love feeling and attachment. He would never do anything I asked him or even the least bit of boyfriend duties. Long story short...

I found out that I'm pregnant back in March when I missed my period. I told him & and was not thrilled at all. He went to the 1st appointment with me and to the 2nd appointment where we learned we're expecting twins. It's like over the last few weeks when I got my 10 week ultrasound & he actually saw them moving and playing on the ultrasound, he actually got excited.. and started to care about me. I know he cared before but it's like now he really wants to be a boyfriend and do whatever to make me happy. I know most women would be excited about that but it bothers me because it seems like I wasn't enough and everything I was doing for him wasn't enough. I think I'm being selfish and thinking it's the babies wellbeing that he actually cares about and maybe he just doesn't want me with anyone else. I really don't know but I asked him why he waited until I got pregnant and his answer was the usual "I really don't know." I just need help understanding this 1. This is my 1st pregnancy so there's a lot I don't understand but this is just beyond me.