This can be tricky, because on the one hand, spending time alone is a healthy and important thing to do. Couples should be able to part ways occasionally and do their own thing, as a way of maintaining their individuality.

But if your partner's suddenly demanding a ton of alone time, it could be a sign they're pulling away. "While needing alone time is normal and healthy, if your partner has to ask you for it, it’s a sign [they might be] becoming frustrated with spending so much time together," Bennett says. "This could indicate second-guessing the relationship."

In this scenario, it may be a good idea to give each other some space, and see if your partner feels better after having an evening alone, or a weekend away with friends. If not, there may be something more going on.

While everyone's entitled to ease into relationships at their own pace, phrases like this one are often a big red flag. "People who are madly in love with each other usually want things to move very quickly," Bennett says. "If your relationship was moving at full speed and your partner suddenly asks to slow it down, it could be a sign of second-guessing."

In a healthy relationship, both partners should be able to focus on themselves and maintain their goals and visions for the future, which is why comments like this one often have an underlying meaning.

"If your partner shifts [their] focus to goals that don’t involve you, it could be a sign of second guessing," Bennett says. "By focusing on [themselves] only, your partner could be setting the stage to move on."

While couples should feel free to point out habits that they find annoying, or things they'd like to see change in their relationship, it's not a great sign if your significant other is suddenly super annoyed by insignificant things.

"Those who are second-guessing their relationship may complain about seemingly small things that were previously not a bother to them," licensed psychologist Dr. Danielle Forshee, tells Bustle.

If they once thought it was endearing that you left dishes in the sink, but now it's rubbing them the wrong way, it may be because they're looking for reasons to back away. You won't know for sure, though, unless you ask.

Your partner may try to test the waters by making comments that hint at a breakup, such as "you deserve someone better than me." It could be a hint, or just a weird way of gauging how you feel.

It could also be a sign they're trying to manipulate you into thinking maybe you could do better, Julia McCurley, a professional matchmaker and founder of Something More, tells Bustle. Whatever the case may be, it's not something you'll want to ignore.

If your partner has been talking about your relationship behind your back — especially if they are taking advice from others who don't have the full story — it's definitely a warning sign.

"You might hear them say that their best friend, their coworker, their therapist, etc., thinks that you should just break up, [that you should] be nicer, etc.," clinical psychologist Linnea Mavrides, PsyD, tells Bustle.

In this case, think hard about whether or not the relationship is worth saving. "Talking through these issues together or with a couples therapist can go a long way toward figuring out if this is something you can work through and build a stronger relationship on," Dr. Mavrides says. But if not, it may be healthier to simply move on.

If your partner is on the fence, they may begin to set up relationship "tests" as a way of helping them figure out what to do. So if they start blaming you for things that seem bizarre, take note.

"They'll have in their mind something along the lines of, 'If they don't text me this morning, it's definitely over,' or 'If we get into a fight on the way to the in-laws again, I know that we should just call it quits,'" Dr. Mavrides says. "These are good signs that someone is looking for a pattern to help them make a decision about the relationship because they are having a hard time deciding if they should actually stay or go. They are looking for a black-or-white answer to help them simplify the complexity of the relationship and force their hand, to some degree."

If your partner is in the habit of making plans without you — for example, they get invited to a party and don't ask you to come along — either they never took the relationship seriously, or they are slowly beginning to check out.

"Whether it's short-term plans or plans for the future, if they intentionally (or even subconsciously) [don't want you to] participate in [their] plans, it may be time for you to reevaluate your relationship," therapist Kimberly Hershenson, LMSW, tells Bustle.

Couples who are invested take each other's schedules into consideration, and make an effort to do things together. As mentioned above, it's 100 percent OK to do things alone. But if it feels like your partner is intentionally leaving you out, you might want to be the one second guessing things.

It's perfectly OK if you partner doesn't want to have sex, or if they haven't been in the mood lately. It doesn't mean your relationship is falling apart, but may simply be a sign they have something on their mind. Part of being in a relationship means navigating these ups and downs, and respecting each other's needs — even if that means not having sex for a while.

It's only worth worrying about if they don't want to talk about it, and are pushing you away. As Hershenson says, "If they are making excuses to not have sex [...] this may be a sign something is up with your relationship."

You can try talking about it again, to see if they are open to explaining what's wrong. If there's no reasonable explanation, however, it may simply be a sign they're having second thoughts.

Keep your eyes peeled for signs of contempt — such as judgmental comments or out-of-the-blue rudeness — since it usually means a relationship may be going downhill.

"If contempt is happening frequently that's a good sign that your relationship is in trouble," Mikela Hallmark, a licensed professional counselor, tells Bustle. "Research shows that the more contempt, the more likely it is that your relationship will end."

So use this moment to speak up. "If you think your partner may be second guessing the relationship it can help to have a conversation about it," Hallmark says. "But prepare yourself. These conversations aren't usually easy." You'll want to ready yourself for whatever they have to say, and make an attempt to keep things civil.

If your partner shuts down and completely stops sharing what's on their mind, that may be one of the biggest signs of all. "For example, if you’re in a relationship and your partner has consistently made it a point to tell you how much they like you, how much they want to see you, or how much they miss you, and they discontinue making these statements, it should be considered a red flag," Dr. Forshee says.

By turning inward and keeping their thoughts to themselves, it may indicate that they're pulling away, or that they're no longer invested in the relationship. But again, it's important not to jump to conclusions.

If you think something's up, talk to your partner first. While having a conversation may not save a doomed relationship, it will allow you to discuss what might be going wrong, or why they might be unhappy, so you can work on improving the relationship together.