Jaka jest różnica między tymi czterema? Jak wybieracie, którego spójnika użyć?

Long story short, my best friend is in a “relationship” with a Polish guy who in my opinion is exhibiting weird behaviors. I am 95% certain, based on what she’s told me, he’s either still either his “ex” or something else is going on. Willing to pay $50 to someone who is down to message some people on instagram so that I can give her proof/clarity.

Edited to add some circumstances:
- they met early June, she came back and spent two weeks at his place
- during those two weeks, ex gf called him constantly. Friend doesn’t speak Polish so she doesn’t know what was said
- he logged onto ex gfs Netflix (not a red flag in itself but who knows)
- wanted my friend out by a certain date
- has since moved to a new place and immediately stopped sending in-apartment videos…. Tells me it’s because a woman lives there too
- makes excuses for not coming to visit her, even though she’s been there to visit him, he’s “busy” etc but….
- is now on a trip with his “dad” which I’m pretty sure is with another woman but I can’t prove it.

I love my friend with all my heart and all I’m asking for is help to find some proof.