I'm 24M living in an Asian country and was last in a relationship about 3 years ago. Since then I've had a few hookups/casual relationships (seeing two girls casually at the moment) but nothing serious. The reason for this was that I was looking for someone mature who I could commit to for a serious long term relationship.

About two months, I found someone close to what I was looking for. Met her at the gym and hit it off right away. The first day we talked for about 1.5hrs and it was obvious there was great chemistry between us. Over the course of the last two months we met about 5-6 times in the gym and talked about 3 hrs in total. Two weeks ago, I gave her my number and asked her to hit me up on the weekend if she wanted to hang out. I feel I was pretty clear that I was asking her out and she visibly blushed but said okay.

Throwback to last weekend I got a message from her (I didn't have her number) and we decided to meet up for dinner at a place I chose. Picked her up from her place and we reached the restaurant. The date itself went great. We were down about 2 pints beer each and making great conversation. I was planning to make a move/go in for a kiss at the end. Eventually the topic moved to relationships and she mentioned her exes and I talked a bit about mine. We were already around 3 hrs into the date when I casually asked why she wasn't dating anyone currently. This is when the shocker comes. She quietly tells me that she is in fact dating a guy since last year and that it's a long distance thing.

I was really taken aback because I thought this was clearly a date and not just two friends hanging out. Because why would she go out for drinks with a guy if she was already dating? I was seriously disgusted and sobered up fast after that. Dropped her home and haven't texted back in the last week. Needless to say, I realized this was a huge red flag and my delusion of her being "the one" broke down real quick. For the next few days I was in a sort of crisis and suffered great mental trauma at having been played like that.

I've calmed down since but it's still on my mind why she would try to pull such a thing. Does she think going out like this with a guy is normal and something friends do? Or is she trying to trade up her bf? I don't want to get into this kind of complication because it is similar to what happened in my last relationship (girl ditched her bf for me) and it was a disaster. Should I straight up ask her what her endgame is? I wouldn't mind staying friends because we'd connected really well - or hooking up with her after a while (when my emotions have totally settled down; though I'm not sure if getting her to cheat on her bf is something I want to do). But I think a relationship is totally out of the picture now.

TLDR; Date who I was serious about failed to mention she was in a relationship until I explicitly asked.