curse of “NO”

many of the times my parents have told me I should learn saying no , because it can be harmful for me considering the society we live in. Although whenever I try to say no for some people’s request. it’s really hard for me I start overthinking the things which are not even true ? I start thinking like , will they abandon me if I say no? or start hating me if I say no to them so eventually even though I’m tired or not feeling well I work for them! just because of fear of losing them it’s painful.