Why do people have to be in a relationship to get a mortgage. I'm single and I have one. I put 15% down.
Well I did say at the end of that sentence you quoted "I don't know where I'm going to end up".
To me a mortgage just seems like a weight around your neck. If you were offered a great job elsewhere or met someone and wanted to move to be with them you'd have a lot of hassle to go through with selling / renting the property.
If however you are at a stage in your life where you have "settled" then it's not such a big deal.