You met a wonderful man, and you both fell in love with each other. He saw you as a mother, he met your DC, his love grew because he saw how wonderful it was and how wonderful a mother you are.
You saw him with his DC and your love for him shrank, maybe just a bit, but you saw his clay feet. You saw that he was willing to put unrealistic expectations on your DC, and you saw that he was hoping the magic of you and your DC would make his and his DC's life better, and didn't mind that at the same time that would make your and your DC's lives that little bit worse.
He's human, snd it's understandable that he wants his and his DC's lives made better by you all in it. But he showed a nasty streak with his behaviour when you weren't willing to completely throw yourself into blending your two families, and protecting your own and holding a little bit apart.
That's not going to change, and I think your love for him will continue to shrink the more you and your DC are put into the position of being "less" so that he and his DC can be "more".
You need to stand strong, this will not magically get better.