feelings about TTC

I've been talking to my boyfriend about starting TTC for over a month now. So I'm in the mindset that no he doesn't want to start yet, we're not ready, whatever. Last night he told me he thinks we're ready. And he wants to start TTC. I've been wanting to hear him say that for so long.. and when he did my heart dropped and I got really scared. I thought my reaction was gonna be excited and happy. But I was in the mindset of waiting... and now everything different. I'm so ready for this. But I guess it took me by surprised. He hasn't really said anything about it since. He tried to have sex with me last night, and I couldn't do it. Because I guess I'm my mind, asking him to pull out would be like me saying no I don't want to start trying, but asking him not to pull out is making it all become so real and make it happening now. And I just need time to adjust, I'm just mumbling. I need some guidance, some advice, someone to talk to..