Another way to react is to make a little joke out of it. You could say 'Hey, are you trying to take over my pencil case?'
If you don't mind sharing your pencil case, you can just let it be. But if it bothers you, you can take the pen out and give it back to him, saying something like 'I think this is yours and I like to keep my pencil case organized with just my own things.'
You could simply and politely ask him why he did that. For example, 'Hey, I noticed you put your pen in my pencil case. Is there a reason?'
Most regular pens are designed to be portable and fit in common pencil cases. However, if your pencil case has compartments that are too narrow or short, or if the pen has some extra - large attachments like a big clip or a thick grip, it might not fit as expected.
A student might have secretly stuck his pen inside his friend's pencil case as a joke. His friend was searching everywhere for the pen until he opened his pencil case and found it there. They both had a good laugh about it later.
You could simply like one of his recent stories if you want to show some reciprocal attention.
I'd say start with a pencil. It's easier to make corrections and adjustments when you're learning.
The expression 'he finds out his wife is story' is not a common one. But if we assume it means he discovers some aspect of his wife that is like a story, he might feel shocked at first. However, he should give his wife the chance to explain. For example, if she has a past relationship that she never told him about and it's now out in the open, he should consider that it was her past and focus on how they can move forward in their current relationship. He could also think about how this new discovery can add depth to their understanding of each other.
Stay calm at first. Reacting impulsively might make things worse. You could casually ask him about the girl in the post later.
Don't overreact right away. You could start by casually asking him how he's been. Maybe he'll mention something about not seeing your stories.
You could try to reach out and ask him directly in a friendly way. For example, say something like 'I noticed you haven't been watching my stories lately. Is everything okay?'.
First, you should find out exactly what 'it' is. If it's something inappropriate or false, you can calmly correct the person and set the record straight.
He should first realize that a gay story is just like any other story about people's lives. He could try to understand the feelings and experiences of the gay characters in the story. Maybe he could even learn something new about love and acceptance. If he has any questions or misunderstandings, he could do some research or talk to people who are more knowledgeable about the gay community.