I was once dropped off early, by a date for being too nice and agreeable. I'm sure my husband would find that laughable.
Someone else broke up with me just a couple of days after asking me to be his girlfriend because I was nice to his buddies when he took me to meet them. We were driving back towards my house when the guy brought it up. I said "That's fine with with me, I don't want to be in a relationship with someone who is going to suspect foul play at every turn". By they time we got to my house he had changed his tune and was back peddling fast. I said "hit the road". He was probably thinking I had been a little too agreeable, too.
That date-cut-short was 12 years ago and the break-up was at least 10. In my heart and mind it was a lifetime ago but the memories are clear. I could list a few other, longer and more meaningful, relationships that I've been involved in but I won't. What I'm really getting at is no matter how deep the relationship currently is, If you don't intend to marry that person you need to get out because you take things with you when you go. The longer you stay in a relationship the more of that person's life leaves with you.
God was serious when He told us to practice abstinence until we married. no matter how much you wish a past relationship away, a lot of it stays in your heart. When two become one, and are then separated, it is like tearing something down the middle. There are still two pieces but each piece takes a part of the other, the edge is jagged. Don't become one with someone you aren't married to and don't separate what has become one (through marriage).
You can change the quality and environment of your marriage before you even meet your spouse by cautiously choosing who to care for and by acting honorably before God and using wisdom in the days that precede your marriage.