Check this out:
https://www.studysmarter.co.uk/explanations/english-literature/american-poetry/sir-philip-sidney/#:~:text=Often%20compared%20to%20William%20Shakespeare,of%20poetry%2C%20among%20other%20works.
The Question and Answer section for Astrophil and Stella is a great resource to ask questions, find answers, and discuss the novel.
Check this out:
https://www.studysmarter.co.uk/explanations/english-literature/american-poetry/sir-philip-sidney/#:~:text=Often%20compared%20to%20William%20Shakespeare,of%20poetry%2C%20among%20other%20works.
Astrophel didn't marry Stella himself because he wasn't in love with her. He didn't realize that he loved her until she was out of his reach...... the wife of another man.
This is interesting but far too detailed for this short answer space.