Scared Baby

[Smoke Jaguar]

It takes strong man not to feel displaced during the first 6 months of a baby's life and a good way to deal with the inevitable feelings of being left out is to really highlight where they CAN help and be an important part of the baby's life.
For instance, my DP knew that bathtime was his thing. For the first few months, too (till I foolishly took over!), he washed and folded the nappies. He got cuddles when DS was calm and quiet, but he knew what his limits were - upset baby needs boob!
To DP's advantage, his younger brother had his son at age 19, then a daughter at 21, and most recently a 3rd child, so he had been there to witness that a daddy DOES become more important to the baby all in good time. Once they realise that there ARE some things that they can't do as well as mummy can, they can take the pressure off themselves and just play the waiting game.
That's not to say that they may as well not be there, I don't mean that at all. Your DS will know who his daddy is and that he is there, he just doesn't need him for his basic survival. He WILL be a very important role model for him in the not too distant future. In a nice balance, at about the time that daddies become more important, mummies don't have to be there as much.
Sometimes, too, no matter how sensitive DP is being, there is nowhere else baby wants to be except with mummy. There's no getting around that. That might help you, too, to realise that when you see DP not being as responsive as you would like, and it might ease your frustration with him. You will need to be his example, and it will take a while to kick in! The last thing you want to do is to make DP feel inadequate. Some daddies also get offended being told that they are not as important and effective as mummy, so us girls have to find sneaky ways to make daddies feel useful I'd start with bathtime - that can be 'their' thing. Also, if you have a sling, or can borrow one, he can carry him when he's calm - just watch his face and body language when he realises that his son has fallen asleep on him! It is such a confidence booster for them, but start out giving DS over when he is calm, or he will feel defeated if he is given an already upset child and can't calm him effectively.
My DS can go to DP for comfort now (still not as good as booby, but he knows that he's safe with DP and that it's a good place to be in his arms).
If your DP can accept that it's just the hardwiring of a baby's brain and body to be so dependant on his mummy (you need to find a nice way to say this!), he will feel alot more part of his life. Your cuddling of DS doesn't cut out DP at all, but I can see how men would easily see it that way.
Do some reading of Pinky, Sheila Kitzinger, Dr Sarah Buckley, if you can, and use what you learn from them to talk to DP. Also, there are some excellent 'Dad' articles here on BB that you could print out for him.
Daddies are very important to babies, just in a different way from mummies for a while, and for very good reason
ETA: this may seem a little airy fairy and tree hugging hippy, but here it is:
Before you talk to DP, sit down by yourself and close your eyes. Remind yourself that you are going to talk to him because you love him and you love your son. You are going to speak from the heart. When you speak from the heart, it's difficult for someone to take offence and call you a smart@rse. Like your mum said, talk about what you have been feeling. Ask him to talk from his heart, too (he might think that's a weird thing to ask, but it should get his defensive walls down). THEN begin the conversation, beginning where you feel comfortable.