He might just not feel like himself again. I mean, we all change once we get into a relationship but to men, losing themself is like losing their pride.
His friends might start to tease him that he has turned into a ‘pussy’ or that he isn’t who he was before because he is now spending too much time with his girlfriend.
Also, if he starts noticing that he’s watched chick flicks with you for five nights in a row, you have a problem.