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Marina Monahar is lovesick – and sick of it.

Monahar studies communications and multimedia at McMaster University. On top of the stress that comes with having a double major, she’s been dealing with the stress of having a romantic interest in someone who blows hot-and-cold.

“We hung out a few times and it was really nice, and we got close – but then things started to get strange once she got comfortable,” she said.

Monahar became involved with the woman in July, and it’s been a rollercoaster ride since. She says things have been getting better, but still worries about the future of the relationship.

“Every time she comes back and is warm again it’s like the best thing in the world,” she said. “(But) sometimes I’m afraid she’s going to leave forever.”

If you haven’t been through it, you’ve seen it in someone else. There are countless songs about it. It’s something we’ve accepted as a facet of modern romance: being inexplicably attached to someone who wants us one moment, then pushes us away the next – but when that call comes again, we’re seemingly powerless to say no.

It doesn’t seem to make sense. When someone we care about hurts us or becomes uninterested, we should want to retreat from that situation. But a lot of the time, we simply don’t.

A Ryerson student, who prefers to remain anonymous (because he says he hopes to still have a chance with the person in question), says he can’t get a certain girl out of his head at the moment. He sees potential in the relationship that he just can’t ignore.

“I felt like we connected, which is why every time she messages me I find it hard not to reply,” he says. “When you connect with someone on a personal level, you don’t want to lose that possibility, even if that person tends to disappear.”

But there’s even more to this phenomenon. As it turns out, science has a lot to do with it.

The partial (or variable) reinforcement effect is a psychological term that explains the addictive nature of uncertainty. In an article for Psychology Today, Susan Whitbourne explains that when we’re in a situation where we are rewarded consistently or where comfort is always there when we need it, we become slower in our responses. Essentially, a reward is sweeter when we don’t know whether or not we’ll get it.

In 1955, researcher A.E. Fisher conducted experiments with puppies, analyzing their behaviour when faced with varying degrees of attention. The puppies were separated into three groups: those in the first group were embraced warmly and comforted whenever they approached the researchers. The second group was punished for approaching researchers. And those in the third group were treated either with kindness or punishment in a sporadic, unpredictable manner. At the end of the study, they found that the third group, who grew up in a world of uncertainty, had formed the strongest attachments to the researchers.

From this experiment, Fisher concluded that, “stress, including the mental stress of uncertainty, is an ingredient in attachment or love, and that perhaps even manifestations of hatred (its polar opposite) somehow enhance love.”

Of course, the relationships and experiences of humans are a little bit different from those of puppies. But both species release the same brain chemicals when faced with excitement and affection. So, suffice to say that we share some of the same emotional instincts as dogs. Feeling animalistic?

In fact, what happens in our brains when we receive only partial reinforcement from a romantic interest can be equated with the rush of an extreme sport, or even gambling – and is one of the reasons people become addicted to these things, according to neuroscientist Billi Gordon of the David Geffen School of Medicine at UCLA. It’s exhilarating when we engage in an activity where we don’t know what to expect or what the outcome might be. Gordon says this is due to the combination of adrenaline and the brain chemical known as dopamine that is triggered in the brain – it creates a feeling we just can’t get enough of.

The psychology works both ways, too. Debbie Hernandez, another Ryerson student, says that if she knows someone is deeply interested in her, she can take longer to reply to them.

“I’m not too concerned about replying right away, because I know they’re so into that they’ll be happy whenever they do get to hear from me. Even if I did take my sweet time.”

Does this mean that we’re destined to be more attached to people who are only there for us some of the time? And could that lost sense of urgency hurt a potentially healthy relationship? Well, not necessarily.

According to Los Angeles sex therapist Christine Milrod of the Society for the Scientific Study of Sexuality, long-term relationships actually create a more balanced release of dopamine, which leads to longer-lasting happiness than that of an intermittent partnership. The addictive stress that comes with an unpredictable lover can become unhealthy if sustained for too long – and a committed, stable relationship proves to lower stress levels overall.

Some of these unpredictable relationships could just be unhealthy habits we need to let go of. Then again, there’s always a chance that hot-and-cold relationship could turn into something more stable. You just have to decide whether it’s worth the fight.

So the next time you get frustrated with your best friend for going back to her ex for the fifth time, give her the benefit of the doubt – it’s nature, after all.

Humanistic halfling who cares about stuff. Ask me what my favourite Pokémon is. Haley graduated from the Ryerson School of Journalism in 2015.