Had this happen to me twice on first dates. It rules, don't listen to your friend cause he's an idiot.
In my experience, the girls were 100% into me. Texted me all the time, begged to see me, told me I was incredibly attractive and sh1t like that. Had chance at sex with them both by the 2nd or 3rd dates. (Didn't proceed though cause I'm still kind of AFC. I felt like I wasn't ready to fvck yet). Then after the 3rd to 5th date.. The girls disappeared.
No contact for a few days, I send them a text or two, no reply or very vague replies.. Then I sent an AFC ultimatum (something along the lines of "Hey, I thought we had something going here.. Or at least it seemed like it. If you're going to act cold like this from now on, then don't bother contacting me again... Probably the worst thing you could do.) and they both called me crazy lol.
The first girl had a fiance in prison who she was still in love with.
The second girl had been engaged (dating this guy for 4 years) and her to be husband cheated on her a month before their marriage date.
I don't like to generalize.. Everyone has a fvcked up moment or two in their life and that doesn't mean they're mentally unstable or BPD, but just look out for those red flags on dates.. And don't hold any expectations until you've been seeing them for a while!
I'd also like to say, girl 2 I royally screwed up on. She saw me out with another girl one night and lost it. From that moment on the frame was in her hands, but we got along great before all that and had a ton in common. She was a real sweetheart, but when she caught me her evil side ran rampant lol. This girl also drove me around to do errands, cleaned my bedroom for me, bought me dinner and drinks, and all sorts of cool stuff.
It's hard to not want to reward them for all this after a few dates cause it seems so kind-hearted. But you gotta watch out. Some of these chicks might be a little crazy!
Enjoy the free drinks in the meantime man!