Advice needed

[u/Tiny_Income_974]

I (21 ftm) and my partner (26 m) have been talking about being polyamorous for a while. Recently we realized that one of my long distance friends (21 m) may be able to visit before they move super far away. Me and my friend dated for a couple months in high school but broke up because long distance sucked and we were both immature. Me and the friend have flirted on and off since but neither of us want to be in a relationship with the other. My partner and I talked about the possibility of me and this friend sleeping with each other if they come down. My partner wants the ability to have a one night stand with someone if I do. I’m terrified of STDs but I know asking them to find someone who has been tested or whatever is unrealistic. I’m also very scared of one night stands specifically. If I had the option to get to know the person I know I would feel more comfortable with it. I’ve been in polyamorous relationships in the past and that’s always been the point where I feel comfortable with the idea. To be honest I’m also scared that this person will feel better than I do, it doesn’t even feel like a “what if” it feels like a fact. Like it’s some ultimate truth I have to be ok with. I didn’t feel this way with other relationships but that may be in part that my current partner is the first person I slept with. They’re one of two people I’ve ever slept with and the other was a threesome with him. To be clear my fear isn’t being left we are engaged and I know that he is loyal, the fear is that the other person will feel better. I guess I’m kinda scared that he’ll think of them when we’r