"...then God would send you someone."*
This is, by far, the most frustrating thing that people have ever said to me, to anyone else, or even to themselves.
I can only assume that it comes from Psalm 37:4 - "Delight yourself in the Lord, and he will give you the desires of your heart." But if you interpret this verse as "be content in Jesus and he will give you all the things you want today", you miss a key interpretation of the verse. What happens when you delight yourself in the Lord? HE becomes the desire of your heart. This verse is by no means an indication that God is a genie waiting to grant your wishes if you can get over the test of delighting in him.
That said... Marriage is a good thing and it's an appropriate thing to desire. God is a relational being; he created us to be relational beings. Marriage is a picture of God's relationship to us. There is nothing shameful at all about wanting marriage.
There is definitely a potential and a tendency to desire marriage for the wrong reasons, and perhaps this is what people mean when they say that you need to be content in Jesus. The challenge is this overlooks the fact that God's blessings are not dependent on us, but are an overflow of his grace in our lives. I've heard stories of people who found someone when they knew they were struggling, and I know single women who are at least as "content" as married women I know.
The tricky thing about contentment is that we live in the tension of the "already but not yet." We are at once in perfect standing with God because of the debt Jesus paid on our behalf and being transformed and renewed while we continue to live as fallen people in a fallen world. Contentment is available... but we are in a place where we are not yet what we will be.
The most contentment that I have experienced is something that the Germans call "Sehnsucht" - it is, paradoxically, "an unsatisfied desire which is itself more desirable than any other satisfaction." (CS Lewis, Surprised by Joy) There is a contentment that comes from knowing there is a certainty to the hope that I have in Christ. This comes with an intense yearning because I do not experience any of it perfectly today. I've experienced it on the drive to work on a beautiful fall day, where I want to bask in the foliage and know that it will all fade within a month's time. I've experienced it when I've been confronted with the sin in my life and it grieves me.
Given the reality of where we are, being here on earth, being in good standing but still not yet experiencing a perfect relationship, it is natural for us to look to the "tangible" things as the final answer to our contentment. "If I could just meet a nice man..." "If I could just get a good job..." "If I could just pay off my student loans..." We have all tricked ourselves that contentment lies just around the next hurdle.
And when I find myself experiencing the desires and the longings that are inherent in singleness (and in being human), I see them as a gift. They remind me that all is not yet as it should be. The best is yet to come.
*Matt Chandler has an amazing bit on this