Here is a list of things that most times causes a good relationship not to last like it should.
1. Loving the person too much or choking your partner with your love - No matter how in-love you both might be, the moment one seems to be choking the other with too much love, it fizzles out the love of the other partner leading his or her love to depreciate. Try to always make it balance or else you just might scare your partner away.
2. Desperation - when you show signs of desperation in your relationship, like trying to trap the person to yourself through marriage, this scares the hell out of some people, especially if your partner is not ready to be hooked up or where the relationship its still in its early stage, don't talk about marriage except if you are both desperate about it.
3. Tight Fisted - As a guy if you are the stingy type, and have never cared about your girlfriend's finances, neither have you bought her any gifts, then I feel sorry for you. Same thing goes for the ladies.
4. Immaturity - No girl wants a childish kid as a boyfriend or someone who talks and does things like a kid.
5. Mode Of Dressing - If your mode of dressing is really horrible, please do something about it fast!
6. Being Untidy - Dirty finger nails and toes nails can also lead to break-ups in relationships.
7. Flirting - Flirting might be fun, and might seem not strong enough to dissolve a relationship, the truth is, it can!
8. Too Demanding - you want this, you want that, you want all. Its better you take a chill pill or else, your partner would definitely get tired of you someday.
9. Lack Of Good Character - When you are too arrogant, too violent, too pushy, always engaging in one fight or the other...this is a big turn-off!
10. Respect your partner's decision always.