If you watched season 2 of HBO’s hit series, “Big Little Lies,” this summer, you know what kind of toll keeping a whopper of a secret can take on one’s mental health. While we all keep little secrets from time to time — and, since we’re being honest, tell lies — it can be difficult to know when disclosing the truth is important, and when it’s best to keep our lips sealed. This is especially true in romantic relationships: When should we let our partner in on something that may hurt them?

Whether you’re keeping a big secret like infidelity or wondering if you should divulge a flirtation you had with someone at work, here’s what you need to know about when you should — and shouldn’t — keep a secret from your S.O.

When you can feel just fine about keeping a secret

Rachel, a 31-year-old woman living in Oakland, California, admits that she’s always been a flirt. “I’ve been married for a few years now, but I still have flirtatious relationships with a few guys I know,” she says. “My husband is aware that I’m like this, and he knows I would never act on it — so I never feel the need to tell him when I engage in these little flirtations, which I consider harmless.”

According to relationship and wellbeing coach Shula Melamed, MA, MPH, these kinds of flirtations usually don’t warrant a big, emotional conversation. “It’s probably not necessary to tell your partner about every person you smile at or find attractive, or even a time when something reminds you of an ex-lover,” she says.

If these thoughts or behaviors are negatively impacting your relationship, however, it may be worth examining why you’re engaging in them at all. “Get an outside opinion on why or how [this is happening] with a therapist or coach,” suggests Melamed.

When it’s absolutely necessary to spill the beans

If you kissed someone else, had sex with them, or are engaging in an emotional relationship that you’re well aware is far from platonic, it’s important to let your partner in on it. They deserve to know about it not just on an emotional level, but also a physical one — when you engage in a sexual relationship with another person, you’re automatically putting them at risk for STIs. “You absolutely have to confess to your partner when you have done something to compromise their health, their livelihood, or your family,” Melamed says.

And if this line seems blurry to you — maybe you and your partner are in an open relationship, for example — it is, at the very least, important that you make sure you’re in agreement about what the rules of your relationship are. “You need to make sure you’re on the same page about things that are OK, not OK, or absolutely unacceptable,” says Melamed.   

What if the secrets you’re keeping don’t have anything to do with your relationship? 

While infidelity or even flirting seem like obvious secrets to question keeping from your partner, other types of secrets are a little harder to unpack. For example, what about an expensive purchase you don’t necessarily want to tell your partner you made, a slipping credit score, or a family function you’d rather not go to?

Melamed notes that it’s important to remember that we’re all entitled to keep certain things to ourselves, especially if they don’t directly have to do with another person. But some secrets can cause shame to build up over time, which can be detrimental to your relationship. 

“Why not tell your partner that you bought something expensive and you feel you really needed that item to satisfy a need? Why not tell them your credit score is slipping and share how you plan on fixing it?” she asks. “If you don’t want to go to a function because you need some time to yourself or just aren’t up for it, doesn’t letting them know or having a conversation where you set some boundaries feel more honorable?”

The most likely outcome of coming clean about these types of things, according to Melamed, is that you and your partner will grow closer and learn to communicate better

When keeping a secret is getting you down

If keeping a secret from our partner is causing anxiety, depression, and problems in your relationship, well, that makes sense: There’s quite a bit of research out there that has found that keeping secrets is associated with worse health and a lowered sense of wellbeing. 

Sarah, a 32-year-old woman living in Oregon, says that for her, even keeping so-called harmless secrets from her partner can feel like a huge burden. “I hate feeling like I have to hide something from him, or worry that he’ll discover my secret at any moment and I’ll have to explain myself. So even if the secret is a ‘small’ one, it makes me feel better to just tell him what’s going on.”

Melamed says that while you should never feel the need to share everything you’re feeling with your partner 24/7, it is important to examine how secret-keeping is affecting your mental health, especially because it could lead to harmful behaviors, both for yourself and your relationship,  down the road. “Secrets can make one feel overburdened, guilty, or dishonest, and these feelings are best examined with the help of a professional,” she says. “This is especially true when they start leading to behaviors such as lying, cheating, or putting one’s self and/or others at risk.”

The main takeaway? If you’re OK with keeping secrets from your partner that they don’t really need to know — like when you smile at an attractive stranger — that’s just fine. If it’s weighing you down, though, it may be worth examining why — and if it’s that bothersome to you, why you’re participating in that behavior at all.