Whether or not you think Severus and Lily had a good friendship is irrelevant to the simple fact that Snape DID love Lily. This is indisputable canon.

A person who has obsessive or toxic love towards another is unable to cast a patronus. J.K. Rowling called Snape’s feelings towards Lily love.

While it is unclear whether this was platonic or romantic love, it is there, it is not obsessive/possessive love and people in this fandom need to accept it.