Well if it helps, when I finally had my dd... I spoiled the child absolutely rotten... and she didn't even sit up until 10 months. lol. She just realized if she screamed and lifted her arms up in the air, I would come running and move her where she wanted to go or hold her. There was no reason for her to sit up, crawl or walk. So, babies are all different in how they develop. You haven't broken him. He is just on his own little path.
Also, you will set the example for people. I make sure when people are complementing the girls that they also complement my ds. If they don't... I will add it in. I rarely feel it necessary though... most people probably complement him more, because he is so sweet and loving to them.
Being mommy is hard... it really is just difficult. You do the best that you can and at the end of the day that is all you can do. There is no way to be perfect. If you go to bed 1 night worried your 2nd ds didn't get enough attention, make a plan to show him the next day how much you love him. Just sit with him and hug on him.
Im sorry you are having such a hard time. I think it will get better... you will do great with your new dd. I really think having my daughter allowed me to be an even better mom to my ds, because I couldn then totally except his boyishness. I can really get excited about soccer and football and cars and starwars, etc. lol.
You will find your way!!