Obligatory sorry for mobile

So my gf left me the day before my birthday. I had recently gone to uni and she couldn't handle the distance. She claimed to loved me a lot and wanted me to be the one, and I loved her to bits, but it was a mutual break up as the distance was soul crushing.

That night, I spent the early hours of my 19th birthday opening 2 gashes ln my lower stomach. It's dark, but you get the idea on the feelings I had for this girl (I don't want sympathy, I'm doing better now that my meds have kicked in).

The break up went pretty smooth and I have been managing since, although there definitely still are feelings, I know it was for the best.

Well it's now 2 weeks later, and I learned that she's sleeping with a work colleague. It felt a bit off, and I don't feel jealous, but it felt a bit disrespectful that after 2 weeks she jumps into hooking up with friends. I told her how I felt, and she started getting super defensive and gaslighting me saying I have no right to involve myself in this and we're no longer together I can do whatever I want. And I get that, she can do what she wants. 

But I feel completely betrayed, the fact she gets so defensive and tell me she wishes she didn't tell me and blames me for how I feel tells me that she knew it wasn't right to do that so soon. And it makes me feel that the whole 2 years of relationship we had was more about attention (which was a long suspicion I had but put out of mind, and this suspicion was well-founded) than it was genuine feelings.

Learning this has made me feel like I don't know her anymore and has really torn me apart a second time since the break-up. I get she can do what she wants, but 2 weeks, I feel, is way too short to be respectful to feelings the other person may still have, and the way she manipulatively defended it feels like the whole relationship was just superficial. 

I feel like I don't know who she really is anymore.

I don't know. AITA?