Many people have different attitudes to its use. Others will demand you use the term BL/boy's love as they do in Japan, some will say it covers all m/m relationships, but most follow the above description.
Shounen-ai is NOT the same term as boys' love.
The current common usage of shounen-ai in Japan is to refer to adults who like young boys (i.e. pedophiles).
Shounenai, like Tanbi, is no longer written. It was replaced by BL (Boys' Love) which are much more likely to have happy endings & have less drama.