Ugh gross. I'm sorry, I've been there with unwanted attention from a boss. Best thing you can do is avoid the personal talk. Come up with some useful phrases you can pull out if needed. Suggestions: "What do you mean by that?" Polite and genuine inquiry that might shake him out of flirtation mode when he's asking you about "trouble". Or sometimes just a blank stare with a terse smile and saying nothing might send the right message that you are strictly business.
Don't feel obligated to reply to late night texts.
Also if things cross a line do not rule out talking to HR. This kind of behavior is absolutely wrong and inappropriate and not something you should feel bad about reporting. His behavior is bad for business.