relationship of convenience

dating someone simply because he or she is around all the time (i.e. conveniently located in your life) rather than having a real romantic connection with them

relationships of convenience are to dating what brute force is to programming - a refuge for the desperate and/or lazy

Andi: He's in all my classes and we see each other every night to do problem sets. So we're dating.

Nizzle: But you don't really like him ... it's just a relationship of convenience.