I Need to Trust, but I’m an Overthinker (gay)

Since around the beginning of our 2 year relationship an issue arose and it involved my partners friend. I was naive back then and I also live to ask question just to know more. I mistakenly asked if his friend and my partner ever had feelings. The answer was no, but they tried going on a few dates. Ultimately they realized they are better as friends. This isn’t very conventional (or at least to me and people around me) and it makes me uncomfortable. It is progressive but I begin to overthink about it when they share a hotel room alone on a friends trip. My partner reassures me but my brain will find a plot hole and run with something that is far from true. What should I do, I really need tips and tricks/advice to not poison my relationship more than I already have. Thanks for listening and I look forward to any and all feedback!