What the f*ck???

OK, I need some help here. I just want to know if I am flying off the handle for nothing. Here is the situation:

I have been "dating" this guy ("Juan") for about 4 months now, exclusively for about 2 (exclusivity that HE asked for, by the way). Of course, the fact that I am not divorced yet has impacted the relationship a bit, because of course that makes me feel like I owe him in some way for putting up with my technically-still-married status, but I digress. But today, Juan decided to tell me his sister is posting an add for him to participate in one women's magazine in a "bachelor of the month" contest. Of course, his sister knows about me (therefore, her brother wouldn't technically be single), and of course she does not care. Of course, now I hate the biotch. WHO THE HELL IS SHE TO INTERVENE IN MY ALREADY-MESSED UP LIFE?????? Also, WHY THE HELL DID JUAN TELL ME THIS???? He is trying to make it as if it was just a "heads-up", a "just-in-case-they-call-me" type of thing, but if it had been the other way around, if a friend had asked me if it was OK to post my profile on a singles' add, he would have been completely and utterly offended and upset.

I just do not believe in sharing when it comes to this. I do not want to be OK with this. I know that nothing has happened yet, but why could he not just told his sister that he was not interested and not tell me this? I just think that, even in the most honest relationships, there are some things better left untold, just to protect the other person. It would not be a lie, just blissful ignorance for the other. Like when a stupid relative says something mean about the person one is dating, but you keep quiet to avoid that person from being hurt. I just do not believe in hurting people unnecessarily. Of course, there are some things that must be spoken and talked about, but in my opinion, this was just one of those things that I would have rather not known. Now, I am doubting whether I should keep seing this guy, since he seems to be open to "new experiences". Now, if I ever get to meet the sister in question (which right now I am seriously doubting), I will be slapping her around in my head.