Sometimes when it comes to addressing red flags, it can be equally as important to know what you are looking for; to identify the green lights. Government officials responsible for uncovering counterfeit money spend a lot more time looking at the real stuff than the fake.
Several behaviors will be important in a healthy marriage. A person needs to be balanced. It's often easy to get imbalanced in one direction or the other; to be too carefree or too serious, too flexible or too structured, too strict or too lenient. It will be important to find someone who is forgiving, responsible, encouraging, honest, admits mistakes, sets boundaries, and can confront you constructively.
These behaviors will likely reflect hearts that feel loved and safe. They will come from people who understand their imperfections, have experienced true forgiveness, and are committed to growth in their own lives. From people who have a deep sense of connection, who understand why God placed them here on planet earth, and want to carry that out. Remember, no one's perfect, but looking for character and godliness may end up being more important allies to you than the goose bumps from romance felt right now.
Think of marital love as a house. Psalm 127:1 says, "Unless the Lord builds the house, those who build it labor in vain." Homes are made up of different parts in much the same way that marriage is made up of different loves. The Greeks used different words to describe love.
All four loves are needed in marriage. Eliminate any and the relationship will suffer. But without the foundation (agape love), the rest of the house will crumble. If you have a leak in the roof (eros love), its not pleasant, but you don't need to junk the house. Make sure that you have the foundation, frame, and roof complete before marriage, so that you can move the furniture in after the closing.