When I contemplate the members of my social network, I am mostly filled with unadulterated feelings of love and warmth: I simply can’t wait to see them again, in the knowledge that we will bask in mutual affection and support.

A handful, however, arouse quite different emotions – a mixture of eagerness and dread. They promise encounters that are the conversational equivalent of Russian roulette. In the right mood, these individuals can deliver a fun-filled evening, but if I catch them at the wrong moment, they can drain me of all my goodwill. There is simply no knowing what is to come.

If this sounds familiar, then you too have frenemies. Psychologists call them “ambivalent relationships” and they don’t just have the potential to ruin a good party, they also have surprising consequences for your well-being. According to a wealth of research, these love-hate relationships are often more stressful than interactions with people who are consistently nasty. They can damage your mental and physical health. They might also be prematurely ageing you.

Knowing this, the simple solution would seem to be to cut ties with these people. But our relationships with frenemies aren’t simple, and ditching them isn’t always possible or even desirable. However, a deeper insight into your ambivalent relationships will help you deal with them more effectively. It could make you a better friend, too. Because, when you know the signs to look out for, you might discover that the frenemy in some of your relationships is you.

Since the 1970s, huge studies examining thousands of…