Purpose is one of the key things that keep a relationship going and healthy, purpose is knowing that you have a reason for living. A reason to live together. Many relationship out there lack purpose. Most youths these days just start a relationship for the fun of it. Nothing is keeping them busy, no important reason for their being in relationship, except that they just feel like being in a relationship with someone or probably to satisfy their sexual urge. Note: once the purpose of a thing is not known, abuse is definitely inevitable.
Please know that it is important that you know your individual purposes and that of your relationship. God is a God of purpose and everything he does or orchestrates is for a purpose. The primary purpose of any godly relationship must be for Marriage (So don't even start any relationship you know will not lead to marriage), and there are also other reasons God is prompting you to start a relationship and you must be dutiful enough to inquire of God these reasons. If you check this scripture "Then the Spirit said unto Philip, Go near, and join thyself to this chariot." (Acts 8:29), you will discover that the reason God orchestrated the relationship between the eunuch and Philip is to help the eunuch. So also one of the reasons God lead us into a relationship is to help us get better and also to prepare us for the future. So dear friends, it is better you discover your purpose early enough. Ladies, it is also very important you ask from any guy that proposes to you his purpose, the reason he want to marry you and so on. Adam had a purpose before he started a relationship with eve (Genesis 2:7-8). Discovering your purpose early enough will help whoever lady God is bringing into your life to fit into such purpose and also prepare herself for the purpose(Remember she's meant to be a help suitable for you, Gen 2:18). Also purpose help you to be focus and also to overcome challenges that may show up along the way in the relationship. It was purpose that made Jesus to endure the challenges/shame he faced on the cross of Calvary (Heb 12:2).