fossball says:
... Going out at night (again) might be more difficult ...
You have your own room. It is not the most private room, so you may be noticed, but going out should be easy enough... and you would only be noticed by servants.
fossball says:
... Especially sneaking to Marisella ...
You would need to find her room. How would you do that?
fossball says:
... he would not want to bring het virtue in danger ...
Indeed. You would need to be discrete in your asking around or searching, and then, possibly public in your talking?
fossball says:
... Altough he suspects she would be even more eager to join the party ...
You are not wrong. If that is an option you may need to cancel the public part of your talking, and be even more discrete in your searching.
If the players decide that that is a thing the might do, we can have the character's action lead to them to discovering which room is hers without obvious questions (how? chance overheard conversation? sneaking around and watching as she goes to her room? something else?). There will be dice, and the decision to take her with you somewhere would be up to the characters when it comes up.