Q: My boss asks me to stay late most nights, and he just talks to me for hours about non-work related things.

A: A consultation may be worthwhile to discuss the issues here.

A: A consultation is a great idea.

There is no guarantee of no retaliation. But the positive is that retaliation claims are possibly the very best ones. Assuming you have a human resources department or a policy for reporting you should follow it. They will investigate it almost certainly. If they don't you can always take it to the EEOC but seeking legal counsel before you do that is strongly encouraged. Going to the EEOC should prevent retaliation but if you go that route you will probably have decided to work someplace else anyway. If there is no possibility of transferring you to another department and the behavior does not stop you may leave anyway.

If you have responded to texts, e-mails, etc... which are not work related stop doing so. Don't post anything anywhere about your workplace, especially not with details. No FaceBook, etc...

No drinks or socializing outside work unless many other people are there. Don't go anywhere alone with this person. Assuming you are not exempt from overtime you should be paid for every minute of time beyond 40 hours per week - even if you are paid a salary. It's amazing how many employees are paid salaries when the law requires them to be compensated hourly plus overtime. These can be great claims. Seek a lawyer to help you.

Keep a notebook. Record what was discussed, the specific topics discussed, dates, times, etc... after every one of these late night sessions. Severe or pervasive sounds like a lot but you may be able to prove it with the specific comments or incidents you relay especially if other employees have complained. You may not be the first and a good lawyer will reach out to others who may have experienced what you are going through. Good luck.