Cancels your dates: Now, we aren't saying that you need be worried the first time your boyfriend/girlfriend opts, but when it becomes a regular occurrence you definitely need to know the reason behind it. When you plan a date well in advance there's no reason why your partner has to be out working late that very day.
Wants to go out only in a group: Hanging out with friends actually helps a couple's relationship. However, when your partner refuses to plan a single solo date, you should question him about it. Like you shouldn't cut off your friends once you start dating, they shouldn't be the reason you get to hang out with your partner.
Ask you to 'connect' with your friends more often: When your girlfriend/boyfriend wants you to hang out with 'your' friends and not 'his' friends, that should get you thinking. Of course, you shouldn't obsess over getting friendly with his friends, but you should have some mutual friends.
No PDA please: Has simple things like holding hands or a peck on the cheek started embarrassing your boyfriend/girlfriend? It's time you figure out what happened to that 'I-can't-get-enough-of-you' phase.
Gets upset when you try to get intimate:
Does she always complain of a headache? Or does he always say he's too tired? If your partner comes up with such flimsy excuses almost every night then you really need to know what happened to that 'spark' between you.
Keeps you waiting... and waiting... If you find him putting you on hold and then forgetting to get back it means you aren't on his mind. Don't be foolish enough to wait for him for an hour to pick up the phone, instead go have a face-to-face chat with him.
Doesn't bother returning your calls: If/she refuses to revert to your calls and messages, it means you can't look the other way and hope that he/she changes her attitude. Your partner can't take you for granted and you have to tell him/her that clearly.
Needs some more 'space': When he/she starts inserting words like 'lack of space' very often while talking about your relationship, you should take some time out to do some re-thinking.
Refuses to discuss future: If your partner is unsure whether he wants to be with you for long, he is less likely to speak about a scenario involving the two of you in the future. If he refuses to move ahead, then maybe it's time for you to move on.
Calls you fat! Now that's hitting below the belt. If your girlfriend/boyfriend keeps making demands that you get a makeover, maybe you should ask him/her to get a new partner.