not taking no for an answer!

So I left my child's dad after I found out I was pregnant and he had cheated on me for the 3rd time. Well, I've decided through my pregnancy that I don't want to keep him from the baby (unless he gave me a reason) just because our relationship didn't work. Well, he hounds me 24/7 about getting back together. He will freak out if I don't answer his text fast enough, or if I don't talk to him all throughout the day. We just talked on the phone last week and I told him I didn't want a relationship besides being parents to our son, he said okay at the time. But literally TWO days later he is commenting on all of my post saying I love you, calling me baby, asking when we can start building again...it's like he FORGOT the conversation I just had with him. It's like he won't take no for a freaking answer. It makes me uncomfortable. And anytime I say it won't work he breaks down and says I'm the only person he has there is no reason to live anymore etc. now he is texting me tonight asking if he can talk about "us" I said yes because I figured it's a good time to set the record straight AGAIN for the hundredth time that I don't want a relationship like that with him, I told him I'd message him after my shower and we can talk. He replied with "thank you, I love you so much and I just want you to know that I'm going to do whatever it takes to get you back" I already know this is going to turn into an argument when I say that's not what I want. I DONT KNOW HOW TO GET IT THROUGH TO HIM. Please anything will help! I just need some advice before I talk to him in a little bit, this is really stressing me out. And our son is due in 9 days so I don't want a big blow up to happen and then have a negative time while being in labor. Sorry for the long story I just don't know what to do, I'm at a loss.