Is it bad for me to feel grossed out or uneasy at the thought of my partner having had recent intercourse with another partner prior to us having intercourse? And I mean within the same day. It makes me feel dirty and like I’m getting sloppy seconds.

I don’t think any feeling is ever “bad,” so to speak. It is okay to feel grossed out or uneasy. If you use those feelings as an excuse to act in a way that hurts yourself or others, that’s a problem - but that’s about behavior, not feelings. I’ve found that it’s best to try to understand feelings and recognize where they are coming from and how I can work on or with them rather than deciding I “shouldn’t” feel them and try to turn them off.

I must confess that I also have this feeling sometimes! Even though I’m deeply secure in my poly identity, and I also have a really high sex drive and don’t feel shameful or gross about having lots of sex with lots of partners, I still feel kinda squicky sometimes about having sex with multiple different people in a short time frame. That doesn’t make me sex negative, or bad at poly. It’s just a feeling I have. It may be somewhat irrational, and it may be informed by internalized shame, but find me a person who never has irrational feelings and is entirely immune to our culture’s messages about sex and bodies, and I will eat a shoe.

If this isn’t creating issues between you and your partner, it’s not really an issue. If there are circumstances that make you feel not-so-into-sex, then do other things with your partner until your personal time window closes on “recent.” If this is causing issues - if you feel repulsed or disgusted in a way that is impacting your sex life with them, or if they have been frustrated or hurt by your reluctance to have sex with them in that time window, that’s something to work on.

I personally think that “I totally don’t mind if you have sex with other people, but give it a sleep and a shower before having sex with me” is a very reasonable boundary, but your partner may feel different, and that’s okay. It’s okay to try and talk about this with them - try not to use shaming language like “dirty,” but just make it about your preferences. “I’d prefer that, if you’ve recently had sex with someone else, you take a shower before we have sex,” replacing “take a shower” with “give it a day” or “use a condom” or “let’s don’t do [certain type of sex] within [time window]“ - whatever helps your mind set a barrier. The good thing about feelings that can seem irrational or arbitrary is that sometimes they can be soothed with equally arbitrary things! Finding a way to soothe and gently put aside these feelings is something you have a right to do, and if your partner isn’t willing to make a compromise for your comfort, that’s a bigger conversation to have.