...one thats relatively new to me, has anyone had to deal with the idea that their partner is "dirty" or bad in any way after having slept with another partner and being turned off by them? Usually I can see the growth opportunities involved in working thru issues, but this one seems so certain, and I'm not really sure of the cause.
I think maybe we need more info, like how long you've been with your partner and in a poly arrangement, do you have multiple partners as well or just the one, you and your partner's gender and orientation, if you live together, and stuff like that. Anyway...
You say this is a fairly recent feeling, so has there been any changes lately? Has your partner started seeing someone new? Have there been changes to your dynamic? Did someone you know say something that inadvertently poisoned your thoughts on the whole thing? Is there anything in your environment that has recently impacted you in a way that has you judging stuff more critically? Do these thoughts only come up immediately after your partner comes back from a date, or just in general? If it's right after returnig from a date, I don't think it's that uncommon to be a little turned off (tho some folks might be turned on). A lot of polyfolk give themselves a period of time in between partners to make the transition from one to the other.
Generally, if one thinks someone is "dirty" for having sex with someone, I would think that there is an overall attitude that says sex itself is something dirty, so anyone who takes part in it... but if your partner is a woman, there might be some of that societally-influenced judging going on in you about what it means if a woman likes sex, you obviously know the stereotypes otherwise you wouldn't have titled this thread as you did.
Another aspect to consider is this: what do you feel about yourself when you think these thoughts about your partner? When you think they are dirty, does that automatically elevate you because you are not dirty? Or do you use those thoughts against yourself somehow and feel like you are dirty, too? Is there something about how it reflects on you to be with a partner "like that?"
Just asking these questions to possibly help you unravel where it's coming from, because often times just having that awareness does a huge amount to help dissipate uncomfortable feelings like that.