Don't know whether I am right or wrong, but I was thinking about two things - the promise & Suju female getup. I can think of the below reason. You all can think and add/comment. Lets see if we can make sense.😊
1) Suju asking Jo for promise - I think Suju here is thinking like Moti. Moti told Jo not to talk about her meeting with Suju because it can harm their improving relationship and the trust between them. Maybe Suju thinks the same too. He might be thinking that Jo is his sister no doubt, but also Shahenshah's begum and begum of Sultanat. If she meets him, then she can be termed 'gaddar' plus the relationship between Jo-Jallu can get hurt. Maybe to protect her from this, he took promise.
2) Suju ne female getup - Now in yesterday's second Jo-Suju meeting, Suju clearly told Jo that this is their last meeting and now they would not meet. Maybe he got some more information that he wanted to share with Jo. Since Jo will not come, he thought of going. This is one theory, Another possibility can lie in today's episode - harem lafda gets blown up and this reaches Suju's ears and he comes to meet Jo to see if she fine.