1. They’re Manipulative
This is the biggest one. Both women and men do it. I see it all the time — someone getting a man to buy dinner or drinks with no interest of getting to know the person, or a man expecting sex for doing so. Manipulative behavior is often not seen at first because of the initial superficial interactions and the “puppy love” effect. Manipulation is when someone acts or uses something or someone with a maleficent or aggressive intention in order to induce a desired action. Manipulation is emotional abuse (Fjeltstad, 2014).
Other big ones to watch out for:
a) Guilt tripping someone into doing something they don’t want to do.
b) Intimidation, using fear, or verbal abuse for creating submission for some action.
c) Positive/ Negative Reinforcement (E.g. Only saying I love you only after someone does something “good” or pleasing to the partner).
d) Anyone who “presses your buttons” or uses your insecurities to get you to do what they want you to do.
e) Giving gifts with strings attached or crossing your boundaries often.
Someone who is manipulative must be in control. So If you find these circumstances to be the case, realize that no one deserves to be subjected to this kind of behavior.
2. You, And Only You, Make Them Happy
In a relationship, you should make them happier but you should not be their ultimate source of happiness. Mature and centered people get happiness from themselves and do not have to lay the burden on anyone else for all their happiness. Relationships should increase happiness, but not be the reason for all of it.
3. They Compare Themselves To Others and to You
Your relationship shouldn’t be a sports game of two rival teams. This shows immaturity and insecurity. It’s not who makes more, who is smarter, or who is better at something. It’s about complementing each other and working as a team. As a couple, the two should be different, but still complementary and synergistic in their efforts and love.
Instead of rivals, healthy people in relationships encourage one another and support one another.
4. Bad Interaction with Strangers, Waiters/Waitresses, and Parents
Are they above anyone? Do they talk with someone or do they talk down to someone? They should treat everyone with respect, from the waiter to their parents. Especially their parents. It is a good indicator of how they’ll treat you one day.
5. You Can Disagree Without Having an Argument
Disagreeing should not trigger an argument. Everyone is allowed to have their own opinion and should not be forced to think the same way on any subject. You should be able to disagree but not be mad at the same time. If you find yourself not vocalizing your thoughts to “keep the peace” due to fear of anger, then this is not only a warning sign; it is a major form of manipulation.
6. Lack of Clear Communication
Hiding your needs and not vocalizing your ideas create distrust and are destructive. No intimacy can occur without communication. The book, The Five Love Languages by Gary Chapman discusses various types of communication including physical (i.e. holding hands, cuddling, sex), verbal (constructive compliments and feedback), and others.
That also means that someone is able to share his or her most intimate details. It is a shame that many couples go 20+ years without knowing what the other wants, whether it is in the bedroom or how they want to be treated, because they may be timid to express it. Express it. The other person may not agree, but should be open to the idea at least.
7. Has Low Standards For Himself or Herself
Ultimately they have to respect themselves to have healthy relationships with anyone else. Whether it’s not having proper hygiene or always settling for their unmet needs, a person with low standards is not mature and will not lift and encourage you to have higher standards.
8. Lack of Self-Love
You cannot love anyone until you love yourself. You can’t give someone water from your cup if your cup is empty.
9. Isn’t Supportive in Your Decisions and Dreams
Even if you fail, your significant other should help pick you back up and encourage you to do what you really want to do. They should never hold you back from your dreams and encourage you unconditionally in a positive and constructive way.
10. Tries to “Fix” You or Change You
Later in relationships people often try to make you into the person they want to have instead of who you are. They don’t embrace your faults and quirks, nor do they love and support you through them all unconditionally. If they try to change you, it is usually manipulative. This is different than encouraging you to be on time or growing together to be more responsible. If You want to change and they help you that is fine. But they should not try to change you. You change for yourself, first. They should love you and your quirks and faults, while being supportive of the changes you want to make. Likewise, hopefully the changes you want to make are helping yourself to also be better for your partner! 
