How to know when thicc is phat?

I'm an 28 year old incel and have no idea about women so please help me out here.

Me and my gf are currently long distance since we both went studying abroad. Abroad I met another girl and we kind of started a FWB/Situationship or whatever you call it nowadays. Basically we went on nice small trips around Europe together.

Since the beginning I told her I'm only gonna do this with her if she promises me to not get too attached. Well of course now that she's back in her country she now texts me all the time saying how much she loves me and she wants to move somewhere together etc.

What the fuck should I do? I tried scaring her away by revealing that I'm a blackpilled sub 5 incel but that didn't work. What now? I'm just scared that if I tell her to fuck she's gonna tell my gf.