My “Brother” wants to have sex with me 🤦🏾‍♀️

My “brother” just expressed to me that he is attracted to me and wants to have “fun” . I just want your opinion on this guys . Because I want to tell my family but I don’t want anyone to get upset . He isn’t my blood brother . My older sister is his half sister. Me and my older sister share the same mother . And my older sister and him share the same father, not mother .

Me and him are not close . I’ve probably seen him about 10 times my whole life and I’m 23 . I recently just seen him at my older sisters baby shower the other day and I guess that brought up the feelings. But any thoughts ?!?

***UPDATE***

Thank you guys for all of the advice.

I ended up just telling him that I didn’t feel comfortable engaging in intimate activities with him. He left me alone but feels a little embarrassed as our sister will be bringing our nephew into this world soon and we will continue to see each other for a while.

As far as telling my family . I was really speaking in regards to tell my sister because that is her brother . But I decided to act like this never happened . Unnecessary drama .. and Honestly I don’t take offense to this issue. But thank you guys, just wanted to share the experience !