I have been in a LTR for some time with a girl from the same apartment complex.( No redflags , cooks , fuck her often , 7.5/10)

Was waiting for her to get ready in front of the block when 2 girls approached me saying that they saw me at the gym ( most people from my small city know me since I am one of three people that lift heavy).

The discussion gets to me being a PT sometimes but for 1 person since I am busy with work and uni. I make them a deal with less money to pay/session if they come together and as we swap numbers my LTR comes out the door asking WTF am I doing.

Tell her I will train them at the gym, no biggie since I did this often.

She says in a passive aggressive voice ok. Later that evening we did fuck and everything seemed normal.

Since these 2 girls live in the neighborhood I thought why not drive them there since they'll pay anyway and I always go with the car.

LTR calls me , I tell her I am driving these 2 to the gym with me and ask how is she(had a ok conversation).

Couple hours later she tells me she will go to a guy friend.( I assume she is trying to dread me since she never hanged out with guy friends 1on1)

I play it cool and say "ok have fun, see you later".

Fast forward 2 days , I get home from uni earlier since our professor had some issues to deal with.

Buy her a rose and some chocolate ( usually do this when dread is applied to comfort her "I got options but I stay with you" in a kind of way) ,get home , she has a spare key and usually hangs out at mine , and see my room door closed (weird).

Hear voices inside (obviously a guy voice and my LTR) , try to open the door and see it's locked , ask to open the door ASAP.

She does open it after some minutes ( had a bad gut feeling at this point).

See both of them on the bed and ask her why was the door locked.

Tells me some shitty excuse.

Dude walks out the room and I see her goddamn underwear barely from under the blanket where the dude was sitting ( guess she was in a rush when she heard me come in).

I knew what was going on at this point and this is the part where I want your opinions on how I could've dealt with it better.

Walk the dude outside and tell him thanks , he leaves.

Tell the now ex-LTR to get her things and leave also don't forget the small gift I got her on the way out.

She instantly bursts into tears and swears nothing ever happened but I kept myself cool and asked her to tell me the truth.

She didn't , kept crying , wouldn't leave me alone.

Told her that she is not welcome here anymore and get her stuff. After minutes of crying she agrees and asks me if I'll come later to her or call her. Give her one final hug and the crying ensues again and tells me to not let her go.

I said nothing and told her to leave.

I surprisingly haven't lost my cool the whole time even though so many thoughts were going through my head.

My assumption is that those 2 girls that helped me dread her ( one of them obviously wanted me) backfired hard even if she didn't do anything as she says , I will not tolerate such shit from a LTR.

Feel a little down but it wasn't a particularly long LTR to begin with. I guess this is a lesson that dread can sometimes backfire.

TL;DR Dread LTR , LTR goes to hang out with a guy friend couple days later , caught her after the deed in my own room , she breaks down , I kick her out.