It sounds like you're in a very uncomfortable situation right now. I know how you feel to some extent, as I'm quite afraid I won't fall in love with the one I adore. I can't tell you what to do exactly because I'm not you, so I can't read your feelings exactly as they are. I believe that this is a situation that you must follow your heart in order to make it through. I'm not sure that I have the answer to your problem, but I hope I can at least nudge you in the right direction. Truthfully though, the right decision may be difficult to come by. I understand completely that you want to stay with him because he's the father of your baby, but you have to keep in mind that if you're afraid your feelings for him won't progress, it may be best to avoid a terrible situation in the future. Odds are if you don't really love him, terrible things will happen between you two when you get older and it'll affect your child anyway. If you don't love your boyfriend, it's better to call it off and make peace as soon as possible, rather than farther in the future. Like I said though, I don't know exactly how you feel about him so I'm not really qualified to judge.
There's also the possibility that missing your ex is affecting your feelings for your boyfriend. If it helps, try and hide anything that reminds you of your ex and move on from him. You may find the love for your current boyfriend growing once you're completely over your ex. It takes time to get over someone unfortunately, but it is possible. It may also help to try and find new things for you and your current boyfriend to do. It may help "spark" up your feelings for him.
Overall, this is a situation that you just need to follow your heart in to get through. Unfortunately, love completely clouds rationality. We never choose love, it chooses us. Sometimes following our mind isn't the best way, sometimes we need to follow our heart.
You can always e-mail me if you'd like to talk more. I'd be happy to talk to you.
dylan_dawson@live.ca
<3 Dylan