Your personality can mean disaster for someone not prepared. I digress to ask your age, but I'm fairly sure you're younger than me
Anyways, DO NOT SLEEP WITH HIS FRIEND NOW OR LATER! Have respect for the love that you have given your boy, and don't trample his heart. If ALL you need is dirty talk, then you'll have to sit down and have a heart to heart with him about it. It's not all about what you say, it's in how you say it, and how he UNDERSTANDS it. Make sure this is done now, and you'll alleviate future recurrances (you may have to remind him every now and again, but don't make a big issue out of it). If he can't handle it, then it's something he is not willing to work on, or you just need to find someone better suited for you... NOT HIS MATE!!!