An important dynamic in any relationship is one's general level of contentment in life.
As a single, you are somewhere on the range of contentment. You might be extremely content or very discontented, or anywhere in between.
When people marry, their range of contentment can shift in either direction, or it can stay relatively the same as it was when both parties were single.1 If it's higher post-marriage, then you've found the goldmine. If it's lower, you've unfortunately found the landmine! Before marriage, most anticipate that exchanging rings will lead to the goldmine.
Many factors play into which mine you are likely to strike after marriage. If you experienced a low level of contentment as a single, expecting marriage to propel you to marital bliss probably won't happen. On the other hand, if you are already highly content as a single, you very well may find marriage to be the goldmine. Wherever you're at right now, if you're not content, don't count on marriage to make everything better!
Often there are spiritual and emotional issues that we need to address. If you've encountered pain in your life that hasn't been faced, please take the time to work through it now before marriage. I'm not saying a person who's struggled in life can't be a good spouse, but it often takes more work to get there. Wishing away the hurt isn't going to resolve it. God can help you face the circumstances that were not the way you would have written life's script. God's power, your openness, and often the support of a counselor and community, are key in your move toward wholeness. Jesus said in Matthew 5:4, "Blessed are those who mourn, for they will be comforted." Burying our pain only delays the inevitable.
It's OK to expect your friend to deal with his/her pain before getting married! Imagine two construction workers standing next to the Leaning Tower of Pisa. How silly would it be for one to say to the other, "So when do we start the addition?" The structure needs to be shored up before you can add to it and expect it to survive and thrive over time. Wounds in life happen, often without our vote, but each one of us has a choice about what we do with those pains. If you or your friend needs to work through past pains, do it now before moving forward in your relationship. Needs that either of you have now may look very different after you've addressed those emotional wounds.