and saying I love you needs to be natural let it happen he has a lot to process too new home new baby new life no more quiet time new rules a child who is difficult and again a new one on the way....he needs to grow up a bit and nicely say thank you to your daughter and understand she is just a child and an i love you is gift to not ignore it completely
You said it yourself your child is very defiant negotiates constantly and demanding...to an outsider that simply sounds like a child who doesn't do what is normally expected of a child her age, doesn't listen or respect your words of direction or authority and who is emotionally anxious and attached to your attention...you want your boyfriend to have instant loving feelings towards a child you said is difficult to be around...and it seems (I may be wrong) she may be saying "i love you" during a discipline moment to get away from the discipline and he doesnt feel he should play into it....I could be wrong but his response to you infers that. I can promise you if putting her to bed takes longer than 15-20 minutes at the most she is doing it to take time away from you and him alone time...she knows you are going to bed with him and she wants to delay that as much as possible...I know this from older step kids who have voiced why they drag out bedtime because it signals an end to time with you and only time with your partner and yes as cute as kids are they will do things to take away alone time for you too....that may be his issue with the bedtime...not that you are a good mom putting your kid to bed but it likely taking an hour of your time after which you may be even more tired had it not taken so long
You might go with your boyfriend and see a family counselor, and talk about his judgement of how you treat your daughter. Since you are pregnant by this guy, the two of you have to work out some ways that he can stop being judgemental of your childrearing approach. He will probably find when the baby is his that he feels differently about you giving lots of time to the baby than he does about you giving time and love to your daughter, and maybe he will get that it is normal to nurture a child. But it would be good to see a counselor together too.