what is beside cheating the number one killer of a couple?

Lack of communication

money

Lying or abuse.

finances

If you do not love God you do not have love to give and you can not give what you do not have. God is Love and if you do not have Him you better not have a girlfriend or boyfriend. If you do not have God you do not even love yourself. How can you love any one? God teaches us to love and without Him it is impossible to know what love is, we only know what lust is. Lust of the eyes, lust of the flesh and the pride of life is the three problems that you will continue to live with until you cry out to God for His help. That is just the way we were created. God made us where we can not do anything without Him. If He did not put each breath in us we could not even breath. It takes God to fix all of lifes problems. When you Love Him, He takes all of the bad and uses them for your advantage. He takes the bad and makes something good out of it if you love Him. He blesses His people that obey Him... My husband had a brain tumor and I knew then that God was about to do something great in my life and He did. I saw the power of God heal my husband and He used me to write a book. See how God used a bad thing and matured me and showed me who He is. LOVE never fails, never makes mistakes, it creates and blesses. LOVE can not lie or cheat and steal. You need the LOVE SPIRIT which is God. Then there is no need to worry. Give your life to God right where you are and your battles become His and He has won them already. He can see your future.

I have to say lack of trust and refusal to communicate... Which also linked to the whole cheating aspect of a relationship...

Communication is the bases for majority of problems in marriage...whether it's money, cheating, lying, sex etc....The way we communicate plays a huge role. People communicate in different ways..I suggest reading a book called "The 5 Love Languages" by Gary Chapman ...It's an awesome book and will give anyone who is open understanding how to better communicate to their spouse, fiance or g/f-b/f... I have read it and it has given me the understanding on how important it is to communicate to your spouse. I communicate differently than my wife does and she communicated differently than I do......So we learning(Life long process) on how to communicate in each other's language...

When the person you love has already fallen inlove with someone before you met them but they can't be with the one that they love so they're with you but you know deep down that they are always thinking of that other person. It hurts like hell.

The underlying things that makes marriage last is trust and respect. We have been married for 56 years and have had our ups and downs, but always knowning that if we did certain things we would let the other down has made it work.
Btw, my wife said after we married she wasn't sure what love was and if she loved me, but trust and respect is what pulled us out of temptations to cheat, lie, etc.
I had plenty of women make advances (and I'm sure she has had too) at me over the years--even today, but I always asked myself is it worth destroying what my wife and I have built together?
P.S. For many years now she has said she loves me and I have always known and told her I love her. But love means trust and respect, not just sloppy kisses and overwhelming emotions that come and go.

LYING, honesty is very important, because if you don't have that, your always wondering whether or not your mate is telling you the truth, even little lies, if they can lie about something petty, how do you know they won't lie about something bigger?

That would have to be Sex.

Actually, there are to many to mention. But, ultimately there all revolved around trust.

lack of communication and disrespectful behaviour

Lack of trust! It causes arguments, uncertainty, and can kill a relationship in a night! Any lying, no matter how petty, also murders relationships.

Lack of communication.

There are so many things that can kill it. But communication, open and honest, should keep things going in the right direction.

Lack of honesty, respect and trust. Trust is very important for a couple. Even after cheating, trust can be developed again, but it takes time and commitment.

After cheating I would say the top reasons are ...

Domestic Abuse
Finance
Dishonesty

Money problems. Arguing about financial matters.

abuse....or lying

being smothered...its good you like someone but people need time for other things....give people s p a c e......and maybe bad breath =]

Money

Actually, finances and money issues are the real killer in more cases than infidelity.

selfishness

Money is often an issue, especially for married couples.

For non-married folks I'd guess basic insecurity or lack of trust (whether deserved or not).

Communication problems, financial complications or incompatibility.

If you are asking what breaks up couples the most after infidelity, I would say lies and lack of communication.

Fighting about money issues.

lack of sex

Finances

Money fights. Lack of sex. Unwanted relatives living in your home. Boy there are a lot of things that tie with cheating.

lack of sex

Lack of money.

Jealousy and no trust.

DISHONESTY!!!!!!!!