Wow, I came across these two articles about infidelity a few weeks ago and I was shocked how accurate they are.

They both mention Aries Moon as a big red flag for infidelity, both in men's and women's natal charts. Also, Sagittarius Mars and Capricorn Mars. Very true imo, especially Sagittarius Mars. However, I don't think that despite its bad reputation Aries Moon would be interested in open relationships. They just cheat or break and up move on, jumping hot-headedly from relationship to relationship. Plus, Aries Moon would be too "selfish" to share their partner so to speak. They feel entitled to go out and get what they want, but their partner hell no. Also, they tend to be very territorial, from what I have seen.

I think open relationships are a better fit for those with strong Gemini or Aquarius energy.

I don't agree with everything in the third article (the one about fidelity). It says people with low libido are less likely to cheat and the ones with high libido almost always cheat. Not true in my case. My natal chart is strongly Fire dominant with my Sun, Moon, Venus, Jupiter, Ascendant, and Midheaven being in Fire signs. I have a high libido but I have never cheated in my life and never will. I'm loyal to the bone to my husband.