Hello 6609510
You know, I think that many people go through this.
We are content to have friends of both genders, and for our partners to have friends of both genders, but when we see that some of the 'friends' may want to be more than friends, we start to feel uncomfortable.
I think that this is normal.
Have you tried saying to your 'SO' ~
'You do know that Grizelda (insert the correct name here) fancies you, don't you?
If s/he has noticed, then you could probably discuss the matter and see how you both feel.
If s/he has not noticed, then you could tell them to be careful not to let them get the wrong impression ~ for their sake as much as anything.
S/he has admitted to feeling jealous and hiding it, so s/he is not so very different from you.
Maybe this is a subject that you need to get out in the open. You have agreed that you wouldn't stop your partner seeing friends, but you don't want to start bearing grudges because of your discomfort.
Talk about it. Maybe you will then feel more reassured
