First, I want to say that it seems to me that some of the responses you've gotten so far could be a bit more supportive. I don't think the problem is that you don't want your son to enjoy his daddy. I'm sure you appreciate the bond they have. I think the problem is that you feel completely rejected by him when his daddy is around. And of course that is going to hurt your feelings. You aren't doing ANYTHING wrong.
I understand how you feel about this. My daughter has physically removed me from chairs so her daddy could sit with her instead. I am a stay at home mom as well, so she is with me 24-7. At first, it really hurt my feelings, but now I've come to accept it. Here's how I look at it. Your son may have a "lovie" (favorite blankie or stuffed animal). He needs and wants his lovie, and will always expect it to be there. If he lost it, he would lose his little mind. But if you offer him a new toy, he'll probably drop the lovie to play with the new toy for a while. You know he still adores his lovie. And you know that eventually, he'll want his lovie again. The new toy may get his attention for a while, but you know it could NEVER replace his lovie. In essence, you are his lovie. :) He can push you away and enjoy his daddy because he knows you will always be there, waiting for him. You are a constant. Unlike Daddy, you don't leave. He knows he has to soak up his daddy-time while he can because he knows Daddy is going to leave again.
The other thing I want to say is that, yes, your husband likes it. Mine did, too. I think sometimes daddies feel that they aren't really needed. We (the mommies) take care of our children's needs without assistance and we do it well. For a long time, I know my husband felt as if my daughter didn't care if he was around as long as Mommy was there to take care of her. When she started showing a daddy preference, he was so pleased - and relieved. He felt like she really, truly loved him. He felt that he really had a place in her heart. Especially because she chose him over Mommy (and we all know how important Mommy is!)
I also think that maybe your husband doesn't want to share their time with you since he is gone so much. Maybe he feels that he should get some one-on-one time with your son since you have him all day to yourself. I'm just guessing. Maybe you can talk to your husband and tell him that while you recognize how important daddy-time is, you also want to have family-time. That is how we do it in my house. When my husband gets home from work, I straighten up, make dinner, or make some phone calls and let them have their daddy-time. Then after dinner, we all play together (family-time). Of course, my daughter is almost 2 1/2 now, so it works better now than it did when she was 15-18 months. But it's something you can suggest to your husband and maybe he'll put more effort in including you in the fun (once they've had their separate time).
I wish you luck in dealing with this. It's not childish for you to feel this way. It IS hurtful when someone you love so much rejects you. But answer this question: If your son gets hurt and has the choice of going to Daddy or you, to whom would he go for comfort? I'm willing to bet that it's you. And that right there speaks volumes. So cheer up, Mama. Your son still loves and needs you. :)
All my best!