OP has been growing on me. It might be less terrible if you carefully read this ten-step guide. Maybe you would like to join me after your study session? An alternative solution is to date your friend. May be a bit awkward but wrong it's not. Step 4 Ask the sister on a date. Just ask him about it.
How to Ask Your Friend's Sister on a Date
ClubsauceJun 8, Step 4 Ask the sister on a date. If I was the friend though I would say something "Break her heart, I break your face" or something like that to let you know. Final--HeavenJun 9, It's wrong if you do it without his approval.