Hi T.,
It seems to me that Trevor spends most of the time with you, so therefore has become very attached to you. It is important to teach him to be independent and also allow him to spend time with his father, even if you need to sneak out without letting him know you are leaving. It is important that he learns to play independently without you being there next to him constantly; just reassured him that you are there doing your chores or wherever you need to do. He will eventually come to the conclusion that it's ok to be alone, to play alone, etc. Talk to your husband about spending time with him, reading to him, putting him to bed, bathing him, feeding him. His father plays a very important part of his life too, as he grows older he will need to learn from him too, things that only him will be able to teach him; yes he is also learning from you, but let's just say he will be more complete having learned from both of you. Tell your husband that this will give him the time to build a bond with his son, this is his opportunity to shine to teach and to plant those great memories of the time they share together, and by all means don't forget to spend time with Shelby to (one on one, quality time)
Good Luck!
JC