I dealt with this as well, when I worked part time. I saw the difference between when Daddy came home from work (yay! Running into his arms!) versus Mommy coming home (indifference or crying). Yes that most assuredly hurt my feelings. But it was natural. Because my daughter spent far more time with me. And we take for granted what we have a lot of.

For instance: When we lived at the beach (the glorious Florida beach!) we went and actually played in the sand and in the ocean less than once a month. We didn't appreciate what we had. It was, like, no big deal. Now we've moved, and live FAR from a good beach. Hours and hours away. A whole day's drive away. And you know how excited we get at the prospect of going to even a crappy substitution for a "beach?" 

I bet his reaction to Daddy coming home has everything to do with seeing more of you throughout the day, and possibly the discipline thing too. He plays and interacts with you all day, and then Daddy comes home. It could be worse, though. He could be completely indifferent to his father's arrival, and that would probably be more upsetting than his excitement, right? How nice to see how much your son loves his Daddy! I can understand it hurting your feelings, though. It's hard to see your child giving so much affection to someone else, especially when you're the one who cares for him all day. Maybe Daddy could delve out discipline on the weekends or whatnot and see if that doesn't level out the playing field a bit.... I noticed the same kind of thing was happening with my husband when my daughter was a toddler. She was with me all day, and as soon as Daddy came home, it was fun time! She'd run to him and want to play, and including me in the fun wasn't part of the deal. At first, I didn't want to say anything because my husband is my daughter's stepdad, and I wanted their bond to grow. Eventually, though, I worked it out on my own. I asked him to help out more with the discipline (without telling him it was because of the affection injustice I felt was going on because I decided that was my own issue, and it didn't need to be his too). Within a few weeks, the affection level was pretty even.

My boy did the same thing at that age.  Now that he's five, he revels in giving me kisses and covering me in stickers.  I wouldn't take it too personally.  He's sure to come around on his own.  In the meantime, just keep doing what you're doing.

All kids are like that. He doesn't feel the need to give you loads of hugs and kisses because you're there from the moment he wakes up to the moment he goes to bed. His dad isn't around much because he works, so when he sees him, he's excited and happy because he's missed him. He doesn't need to be excited over you because he knows you'll always be there. He doesn't need to show you he missed you because he hasn't had the chance to do that.

Do a little research, and I'm not being nasty saying this because I have a son as well.  The most significant relationship a person has in life is with the same sex parent.  Your boy needs as much affection and learning time with your husband as he can get.  It's for his benefit, not yours.  Don't feel left out.  Just realize it's keenly important that you have a wonderful, supportive father for this boy, who can role model for him, teach him, play with him, and some day your son will gain many of the same skills.  Relationships do go back and forth, and when they do, you can enjoy this.  But make no mistake, a son needs a very good male role model so he has something to draw from.  My 34 year old son reminded me of that while discussing the fact that his father and I divorced when he was very young.  He said "I never had a father who taught me certain things about life, so I won't make that mistake with my son."  He and his son have the closest relationship right now, playing, bathing, fixing food, in fact, in the hospital, he changed his first diaper, gave the first bath,etc.  I think it will make a difference in my grandon's life, to have a strong father figure.