Clingy 15Month Old Boy

The best thing you can do is to give him tons of love! Let him cling. Give him what he needs. He's still a baby and the world is a scary, confusing place. They all experience separation anxiety around this age, it's very normal. If you can, just be with him all the time. The more love (a.k.a. security) you give him now, the more independent he'll be in the future since he'll know he's got a solid base. Try to see it through his eyes and try to remember that this is a phase and he'll grow out of it (and then you'll miss it! lol!)

I think this is probably separation anxiety. It will pass. Make sure when you do leave that you give him a warning that you are leaving, and that he sees you go. Come back after a short while. Gradually increase the amount you are gone. Do not shame him for crying-- just calmly remind him that when you leave you will always come back. And don't let him see your anxiety about leaving... that will only make it worse.

Sounds like you have a High Need baby just like I did! They can be very tough. My son was like a piece of velcro for the longest time! He'll be 3 in a couple of months & is significantly better now, but is still extremely shy, clingy & favors me to anyone else.
Do you have a good sling? If not, GET ONE! It will be your best friend, I promise!
THING-A-MA-SLING offers a 15% discount in the Marketplace. :-)

Have you ready any Dr. Sears books at all? Lots of great info in them! "Attachment Parenting" & "The Fussy Baby Book" are great ones! www.askDrSear.com also has tons of great info.
Hang in there!

when you leave him with somebody, how do you do it? do you sneak out of the room when he's not looking so that he doesnt miss you immediately? do you tell him you're leaving but will be back soon? do you linger? do you rush out?

My daughter has gone through phases of clinyness. Every baby is different, but for her I found that singing helped calm her down. I'd explain that we'd sing 1 song and then mommy was leaving and that I'd be back after nap or after lunch or whatever (to give her a milestone), We'd sing our song (usually old mcdonald) and I'd say goodbye. Her teacher would then hold her and sing another song, and she'd stop crying soon after I left the room.

Some days went smoother than others, but eventually the dropoffs went without incident.

Try different things to calm him down and reassure him. For my LO, lingering only made things worse, it made her feel that if she kept up the crying spell that I'd stay longer. The singing helped give her an expected routine and calm her down

Good luck!

I whole heartedly agree with Dyreka K.

I am a bit surprised that he won't go to people that he's often with. In the case of the cousin and your mom. I suggest spending more time with him and your cousin and mom so that he will get used to them. Do not try to get him to go to them. Just you and your baby be with them and have a good time together. You're going to need others help you with his care once his sibling arrives.