Any partner who sees their partner suffering and, whether the reason is reasonable or not, says “It’s not my problem. It’s you” is not a partner.
Partnership is about coming together when things are hard, not distancing from it. This is a basic tenet of any good relationship – empathy and compassion for the other person, not to mention if what you are doing is hurting the other person, stopping it. You do not have to accept less than that because you have mental issues.
I think there is something to be said for not being overly anxious or insecure when our significant others have friends they could potentially be attracted to. That being said, though, that doesn’t mean that there isn’t a line in which loyalties end up being compromised. So, I’m not sure that I agree that this is totally our thing to figure out. Some of the activities might seem to be potentially problematic and tiptoeing up to some line of inappropriateness (it’s one of those things where even if you can’t define the line, you sort of recognize it when it shows up). Also, if some of those behaviors are painful to you, they are painful to you, and a good partner will at least try to be sensitive to that rather than say it’s totally your thing to figure out.
Partner’s behavior would make one feel insecure. It doesn’t have to be “is he going to have an affair”; it can just be “is our connection dying on the vine and am I seeing the signs of it in the way he is no longer prioritizing me”.