You should never EVER have a relationship just based on sex. That's the way to live a wrong and immoral life!!! You shouldn't be having sex until marriage. And in a relationship having things common with someone is very important.
How do you know it's gonna be short-term? If you have feelings for them it might turn into a long-term. If you're both adults and you're both okay with just having s e x then heck, I say have fun. But don't be too shocked when feelings develop as you get to know each other more and more every time.
First you must respect yourself enough to be adult and not engage in this activity. ?Get to know yourself better and determine your own "values." ?You are better than this and it is bad karma to "use" others. ?book: The 7 Habits of Highly Effective People by Stephen Covey. Worth reading!
I don't believe in knowingly going into short term relationships, because every time you are in a new relationship you give part of yourself to that person, making a real marriage something flimsy and not special. I think if you know you're not going to stay with that person or marry them, you shouldn't mess around with them or get close to them physically or emotionally. Dating without the intention of marrying is like going to a grocery store with no money, you either leave unhappy or take something that is not yours.
Be true to yourself and true to other people, be genuine and pure. Save yourself for the one love God has for you, and do not settle for less any time along the way.
Short term is fine if that is what you're looking for and you know it's never gonna lead anywhere, but you can't beat being in a loving relationship with someone you share common interest with and love you for being you not just for the sex.