Lesley Arfin is the kickass author of "Dear Diary" a longtime contributor to Vice magazine and one of the raddest girls we know. So it makes sense that we'd go to her for advice. Got a question about love, relationships or that burning sensation?

Q: My friend just started dating a new guy, and she's super-excited about him. The only problem -- he's ALSO dating another friend of mine. Friend B knows that he's seeing other people, but Friend A has NO IDEA that her new dude is sleeping around. Friend A just got out of a long-term monogamous relationship, so she's feeling particularly vulnerable. Should I let Friend A know that her romantic interest is a bit of a man whore, or just stay out of it?

Click here to read Lesley's advice

Normally I would advise you to stay out of the situation, but not on this one. Because it's the very beginning and in the dating stage, you have to have a sit-down with friend A. Are friends A and B friends with each other? I hope not, but I guess you would have mentioned if they were.

Besides saving your friend from potential STDs (I mean, he's "sleeping around"? Sorry, I don't mean to sound square, but this dude doesn't really sound like a winner), you also wrote that your friend is feeling vulnerable. So basically you're asking me if you should stay out of it to avoid a confrontation, and the answer is NO! This is your friend! Put yourself in her shoes and think about how you would feel if she knew this info and didn't tell you. Sit her down and explain what you know. If she gets mad, it's just a defense mechanism -- don't take it personally. In the end she'll thank you. Maybe friend A won't care either way, but at least she'll have all the information to decide that justly.

xox les

Agree with Lesley's advice? Disagree? Tell us in the comments.