I think we've probably all been in an unhealthy relationship, or know someone that has been.  A relationship can be harmful on many levels.  Sometimes overwhelming feelings of love can be enough reason to stay, but that shouldn't be the case.  Here are some comparisons of healthy love and toxic love..

There is no goal to reach that will bring us to happily-ever after. We are not incomplete until we find our soul mate. We are not halves that cannot be whole without a relationship.

True Love is not a painful obsession.
It is not taking a hostage or being a hostage.
It is not all-consuming, isolating, or constricting. Believing we can't be whole or happy without a relationship is unhealthy and leads us to accept deprivation and abuse, and to engage in manipulation, dishonesty, and power struggles.
The type of love we learned about growing up is an addiction, a form of toxic love.

Here is a short list of the characteristics of Love vs. toxic love (compiled with the help of the work of Melody Beattie & Terence Gorski.)

1. Love - Development of self first priority.
Toxic love - Obsession with relationship.

2. Love - Room to grow, expand; desire for other to grow.
Toxic love - Security, comfort in sameness; intensity of need seen as proof of love (may really be fear, insecurity, loneliness)

3. Love - Separate interests; other friends; maintain other meaningful relationships.
Toxic love - Total involvement; limited social life; neglect old friends, interests.

4. Love - Encouragement of each other's expanding; secure in own worth.
Toxic love - Preoccupation with other's behavior; fear of other changing.

5. Love - Appropriate Trust (i.e. trusting partner to behave according to fundamental nature.)
Toxic love - Jealousy; possessiveness; fear of competition; protects "supply."

6. Love - Compromise, negotiation or taking turns at leading. Problem solving together.
Toxic love - Power plays for control; blaming; passive or aggressive manipulation.

7. Love - Embracing of each other's individuality.
Toxic love - Trying to change other to own image.

8. Love - Relationship deals with all aspects of reality.
Toxic love - Relationship is based on delusion and avoidance of the unpleasant.

9. Love - Self-care by both partners; emotional state not dependent on other's mood.
Toxic love - Expectation that one partner will fix and rescue the other.

10. Love - Loving detachment (healthy concern about partner, while letting go.)
Toxic love - Fusion (being obsessed with each other's problems and feelings.)

11. Love - Sex is free choice growing out of caring & friendship.
Toxic love - Pressure around sex due to insecurity, fear & need for immediate gratification.

12. Love - Ability to enjoy being alone.
Toxic love - Unable to endure separation; clinging.

13. Love - Cycle of comfort and contentment.
Toxic love - Cycle of pain and despair.

Love is not supposed to be painful. There is pain involved in any relationship but if it is painful most of the time then something is not working.

LykMagic said: 

Love is not supposed to be painful. There is pain involved in any relationship but if it is painful most of the time then something is not working.

Usually when a person first gets in a relationship for the first year or so everything is absolutely perfect. Maybe all the relationships I've been in have all been really wrong but after the first year of bliss everything seems to fall apart and the love just becomes painful. A friend of mine told me that that is the way it is with marriage too. That the first year they live together its hard but after that it gets better. I can't really tell whether I'm in the wrong relationships or whether if I just stuck it out that all that pain would go away and it would go back to the way it used to be.

    I think you can tell if you're in a good relationship if you really know that person has your very best interest at heart, and also if they truly make you happy.  Some people are good for you, but they may not bring out the very best in you.  I figure there are people that are good for you, some are definitely wrong for you, and then there is that absolutely perfect person for you... but they may only be perfect for a certain period of time, and then things could change, people could change.  But basically you should find the person that makes you the happiest, and is NEVER mean to you! 
    And I've noticed also that things tend to dwell out after the first year.  I guess you always have to keep working on the relationship, always evolving, trying new things, meeting new people... I think people could start getting use to each other, and then the relationship could get boring...?  Idk but I think it's important to appreciate the little things in the relationship and always be reminding them of how you care about them.