Why is this new adopted kitten so needy?

by Kim
(Miami Beach, Florida, USA)

I just adopted a 7-month-old kitten and he is so demanding of attention constantly! He cries when I leave the room. He is all over me all the time and I have another cat that is not too happy about the attention she is missing. She hates him and I don’t want to give him up because I feel bad for him and love him.