I have a similar situation ....I started a child in feb and she was my youngest until oct when I started a 12 month old boy (she is now 18 months). If he comes near her she shreiks but if ge actually touches her or the toy she is playing she totally loses her noodle. She shoves him pushes him .... Has absolutely no tolerance for him at all. I keep telling her we must be nice or he's just looking.
It sound like your little guy might have a bit of separation anxiety or he may have laid claim on you and is showing signs of jealousy.