I have a divorced classmate ... who often asks me out for dinner and sends messages! I'm single now and never take the initiative to find her! She also often goes to the house she rents to chat. ...

If you don't want her to come to you, it's simple. Just say you have a girlfriend, and you are with your girlfriend. This is normal, and it won't hurt the friendship between classmates because you have a girlfriend! However, if you don't want to develop with others, you'd better not fight in your heart and keep your head cool!