Girlfriend had a secret boyfriend the entire time

I was sleeping with and dating a girl for 3 months, 1 month in she confessed to me that she was falling for me, I didn’t feel the same but assured her I probably would

we never had the exclusive discussion but were spending tons of time together and I was happy just keeping things relaxed

About 3 months in I admitted that I had started falling for her too

One day she mentioned that she hadn’t told me the full truth about herself, only half truths - there was something she needed to tell me, it “wasn’t a big deal” but she was worried I wouldn’t like her after she told me

We slept together that afternoon and while lying in bed she revealed to me that she had a long term boyfriend

I told her to get the f*ck out, get lost etc, the whole nine yards, however she didn’t/wouldn’t leave, she just sat there crying (with tearless eyes) telling me how sorry she was

I said to her “even if I continue seeing you you’re going to eventually just crawl back to him aren’t you”. She couldn’t even deny it and just sat there in silence

Over the next few weeks I asked her to leave him and be with me repeatedly and she always just said “I don’t know”, said that she “needed more time to decide”

I was going to stop seeing her but whenever I asked her to answer the question “what/who do you want” she would say she wanted to be with me

In the end I couldn’t take it any more and said that I couldn’t keep seeing her while she was with someone else

And it hurt but didn’t surprise me when she just accepted us not seeing each other as an option

So we arranged one last meet up before we would stop seeing each other

The very last time I saw her I asked if she loved me and she said no which totally blind sided me as the last thing I heard was that she was falling for me a few months ago

Over the next few weeks she didn’t leave him and was still saying she needed more time, we still texted but didn’t see each other in person any more

Her boyfriend then found out about everything and she proceeded to block me on everything, change her number etc

So I’m now sitting here feeling completely broken hearted and betrayed, I’m too close to things to see anything clearly

so my biggest question is did she never actually want anything with me, was I just an outlet for sex and attention and nothing more - I can’t comprehend why someone would do what she has done, if anyone has ever done something similar what were your reasons, did you actually care about or want a relationsip with your affair partner? Or were they just a side piece

EDIT: to clarify when she told me the truth she spun a story of:

We’re not living together, I haven’t even seen him for a month, we haven’t slept together for six months etc etc

So I basically thought they weren’t really dating and were about to split up