It's really hard for me to get K-bug to laugh and giggle but as soon as she sees her uncle she doesn't stop giggling. He is pretty much the only one that can get her to giggle like that.
BF feels the same as you. As soon as he gets home from work she smiles at him but when he picks her up she screams and grabs for me.
Yesterday I was trying to leave for work and had to walk out of the house with K-bug screaming at the top of her lungs because dad had her and she didn't want the bottle she wanted mom. It's days like that it breaks my heart I have to work. I only work 2 days a week too.
I'm sure that he felt how frustrated you were and thats why your mom was able to calm him because she was calm.
I don't think its that he's bored of you...it's just something different. As for your mother being able to calm him...well she's more experienced. Babies can easily pick up on your vibes so if you are feeling what you have expressed in your post, then he probably senses that. I'm FAR better at calming my kids now than I was with my first and second.
Try not to take it personally. Fynn loves you, you're his mommy. I bet if he was seperated from you for hours/days at a time he would be just as happy to see you :)