Girlfriend's sister is too comfortable
Girlfriend's sister has broken up with her boyfriend couple of months ago after finding out that he was cheating on her regularly with a coworker. I found it pity because I liked hanging out with them as two pairs.
Since the breakup, she has been sleeping at our place very often, because it is very close to her work anyway and she needed our company and support.
She has always been comfortable around me before her breakup, I've seen her in the past in her underwear or only in a towel. And I've even seen her topless last year at the beach when I was there with my girlfriend and her, she changed her bikini top in front of me and stayed topless for few minutes while talking to us (they are European).
Now recently this exposure has been much more frequent. While at our place, she's mostly wearing shirts without a bra, multiple times getting undressed to her thong and bra in the living room and a few times even completely topless until she takes her time putting her sleeping shirt on.
She's also joined us few times cuddling on the sofa watching TV, with my girlfriend in the middle.
Yesterday, while I was sitting on the sofa busy on my phone, she layed on the other side, putting her feet on my lap, just like my girlfriend usually does! I looked at her shoked, she smiled and said joking that she's tiered and needs to lay down there and if I mind, I have to sit somewhere else!
I said joking: Sure, it's your place at the end and I'm only a guest! She just got busy on her phone afterwards, after a few minutes I started massaging her feet as I usually do my girlfriend's (she had socks on). She just made a small mmm sound like she likes it. My girlfriend got into the room and just smiled and said dinner is ready do we both got up like nothing is unnormal!