I never want to do it again, I pray to God for the resolve not to never subject myself to it again. Don't date them:
You can't convert them, I've tried
I thought, I wasn't so bad when I was an unbeliever and I eventually converted, so why can't they? You can tell them all about The Truth and they might even agree with you, but they won't retain it or have any interest in it. You realize there was a reason you became/are a believer, something you can't give to others or show them how to find or develop. There conscience is weak, and there lesser impulses are strong, low levels of Holy Spirit.
They do not understand right from wrong
You will be periodically shocked at how self-centered, immature,confused, and misguided they are. The worst part is The Bible has no effect on them, so you can't even reason with them. If you show a Christian a verse that shuns their behavior, they can't argue with The Bible and should be willing to change. With an unbeliever it becomes a battle of emotions, and they will lie and justify their behavior any way they can reason with their worldly faculties.
Worldly Desires Come First, lying, manipulating, anything is permitted
They have no Higher beliefs, all they have is lower ones. There is no higher authority to tell them what they are doing is wrong, so all their actions become about getting what they want. Money, sex, material desires, idol worship, you may be placed below or on equal importance with these things. Your love or hope for love will leave you vulnerable to being manipulated and lied to.
Nothing is Sacred
If you want your marriage and intimacy to be beyond the physical, they have little reason to treat it as such. The divorce, infidelity and single parent rates are high largely to do with God not being involved in these matters. When everything is boiled down to tradition, social pressure, and instinct, you lose everything important and what keeps this things stable and meaningful. Do you want your children to be Christians? An unbeliever parent will test and confuse them.
They have no Way, Truth, or Light
When they experience hardship or are tested, they do not have Christ. They may become depressed, irritable, irrational, angry. When they are tested they may be broken or resort to sin, and who knows if they will find their way out of it. Who knows how they will handle aging or mortality? Will they put their body above their soul they may or may not believe in? Will they take the mark of the beast or adopt liberal policies you don't agree with? Sin will enter your world through them.
Do you want someone to go to Church and Talk about The Bible with?
If you want your faith to be a large part of your life, and beyond a "hobby", you need your partner to actively participate and help you grow. An unbeliever will distract you from your commitments and duties, may even try to get you to abandoned them.
1 Corinthians 15:33
Do not be deceived: “Bad company ruins good morals.”
And you will also be around there heathen friends too.
God doesn't want you to do this, It's very clear in The Bible
Magenta already said it
2 Corinthians 6:14
Do not be unequally yoked with unbelievers. For what partnership has righteousness with lawlessness? Or what fellowship has light with darkness?
They are "great" unbelievers out there you are attracted to, and Christians you are not attracted to. A healthy and strong relationship goes beyond just attraction alone, especially with time, and you need God present in it. You need to find someone you are attracted to that is also a devout Christian, then maybe in this sinful and corrupted world your relationship can stand a chance and you can experience lasting love. And you need all the help you can get to save your soul, you don't want to be attached to a sinner and dragged to hell with them.