You are not happy
This is the number one sign that you are in a very unhealthy relationship. When asked, most couples say the best thing about being in a relationship is the happiness being with the one they love brings.
If you are not happy with your partner or he or she seems not to be happy with you, your relationship isn't healthy for one party and until things change, there will be one unwilling and unhappy partner in that relationship.
There is no trust
A lot of couples check through their other half's phone but the question is, for what? Are you sniffing through? Are you checking to see who they last called/spoke to? Are you checking to know who they regularly send messages to?
If your reason for checking your spouse's phone is to keep tabs on their lives then trust me, everything is wrong with your relationship.
Trust comes with love and the moment you start pulling an FBI on your partner's phone, it means you do not trust them and your love isn't genuine.
I am not a member of that school of thought that says open relationships/marriages are great so for me, when you are with someone that is not your partner then you are cheating.
If both of you cheat on each other and you are still together because you believe nothing can tear you apart, then be ready for a very unhappy journey which begins now.
You don't respect each other
By respect, I don't mean kneeling to give him his coffee/meal, I am talking about respecting his/her wishes/decisions/opinions. I am talking doing the things he/she wants and likes and not acting like they do not exist.
A relationship that lacks respect lacks what it needs to last long. Y'all are closer to rock bottom than you think.
Your relationship is emotionally and physically abusive
For a lot of people, abuse starts and ends with the physical violence. When you are being emotionally abused, then you are as unsafe as the person who is being physically abused. And this is not just for the women, because there are a lot of men out there who are stuck with women who emotionally abuse them.
This is unhealthy for you and it means your relationship, rather than helping you grow is killing you.
You cannot recall the last time you laughed
You certainly remember the times when he/she made you mad, made you sad and made you worthless but the good times? That must be ages ago.
Your quarrels, fights and misunderstandings have overshadowed your happy moments and these days if he is not the one mad at you for something, you are the one mad at him for something.
Maybe its time to fix it or kill it, you have to decide now.
You never communicate
You just realize that these days, you both never say anything to each other anymore. Conversations are empty, you don't desperately need each other's company and you don't look forward to discussing anything with each other.
Maybe this needs to rest?
There are a million and one signs that show you are in a relationship that is unsafe for your health and if you listened carefully, you would see the signs screaming at you. Take these signs seriously and take the needed steps towards whatever decision you have decided to take.