I tend to look inward on these things first. So step one, I'd ask myself are you flirting with others? If the answer is no then you can proceed directly to challenging your partner for something that has zero basis in reality. If the answer is yes then I would assess how serious I consider that behaviour to be, how it could be construed by others, and whether or not my partner may justifiably feel upset by it. Armed with that I'd then go ahead and have the conversation with my partner, but be willing to accept some responsibility for making them feel insecure.

I think self-reflection is almost non-existent nowadays, but it's a useful trait to develop because it allows you to operate from a position of integrity and know you've challenged yourself about your role in a given issue.