the reasons, i think are both the ones you put forward. lots of good sex and exploring bdsm.
as for what you should do---
do get to know your new friend. she could be a great source of bdsm technique/resources. that said, bdsm contains a lot of knowledge, and a lot of styles. what works for her may not work for you.
bdsm is best when you are honest with your desires. tell him the story about meeting this girl, and tell him how it made you feel. but tell him that you wanted to talk to him about these feelings since you've not felt this before. but have no expectations. ask him what he makes of it. be willing to give up the idea of doing anything with the classmate.
infact, don't wed yourself to play with her at all. think about the fantasies you've had recently, talk to mr. about them, and think about where you want to go, and what you guys want to do, but DON'T make her the focus. this should be about you and pugs, absent of this new temptress.
i don't know if you guys have set up avenues of negotiation, just a time where you sit down and say what you like and don't. feedback is important for both parties--especially after play. this could be aftercare, or something when neither of you is in a dom/sub role--or not-- just a time when you can talk directly. it's good to have a regular interval where you just check in and talk.
bringing someone in to a relationship can be very dangerous, no matter how strong the relationship. it is important that you:
1)take it slow
2)listen, respect and honor the wishes of your partner
3)they need to do the same
4)be honest with yourself and your partner
5)they need to do the same.
that said it is still never fool proof. so talk. be specific. be honest.
my rules for bringing someone in is that the partner makes the rules. even if it's non-sexual bdsm play. if something makes them uncomfortable, they get to trump your lust. so:
if me and my gf do bdsm and i love sucking dick, and she has a foot fetish, i may feel threatened by her worshiping some other girl's feet. so it is my call if we are "foot fetish monongomous." that said, i may not care if she sleeps with guys, but no trannys or gennys (genetic girls) or i may be fine with that. she may say, that i can look, touch but not have a dick in my mouth unless she is there. she may say that i can only have strap ons, or whatever she deems. i have had rules where my gf could sleep w/guys, but could not spend the night. or had to give me 24 hour notice, or i had to meet the guy first. and rules should be able to be changed at anytime if your partner feels wrong about it. the point is to make your partner as comfortable with this as possible, and show them you will follow the rules they set and they don't have any reason to worry, you can be trusted. but starting out, i would not recommend sex, i would go for non-sexual play, until you are both used to talking honestly.
for a good detailed list of most kinds of play, again i recommend bondage.com's profile questionares. they can be set to private so no one can see them but you and your partner, and i would bet there are some things you've never thought or heard of. sure to get the creative juices flowing.
IF you are trying to keep a bad relationship together by opening it up: this is a bad idea.
IF you are worried about him cheating or vice versa: this is a bad idea.
IF you already have cheating issues(someone's cheated): this is a bad idea.
open relationships are not for everyone. but if you are looking for non-sexual bdsm, the above rules should suit you. but take it slow. for the first year, don't do anything you would feel uncomfortable knowing your partner would do. do some reading.
do get to know your new friend. she could be a great source of bdsm technique/resources. that said, bdsm contains a lot of knowledge, and a lot of styles. what works for her may not work for you. as with any bdsm activity, research, research, research!
one book i would recommend is the ethical slut.
linky:wiki:ethical slutamazon: ethical slut