I think it’s the better choice for both of them.
He could say that living together just doesn’t feel right to him yet, and he’s afraid that doing it even though he’s uncomfortable about it might hurt the relationship long-term. This is probably the truth.
I’m so glad my boyfriend and I are living separately. Post-graduation life is an insane transition. Suddenly having an adult paycheck and bank account, commuting, maintaining a real apartment, getting used to a full time job, being away from my parents a permanent way, making friends and connections in an enormous city… I don’t know how it would’ve worked if I had also combined the newness of splitting finances with my boyfriend, living together, getting used to each other’s morning/night routines, seeing each other all day every day… it would’ve been a LOT at once to deal with. Also, as much as I love spending time with him, I really like living with roommates right now. We potentially have the rest of our life to live together; it’s kind of nice having this period of independence for now.
@HiMom, I did not mean he should move in to avoid offense, I meant, I wonder if we old CC parents can help him come up with some good ways to explain it that help the other person leave the discussion not feeling rejected.
I think it would be a good goal to hope she feels respected when they are done speaking. GF, I do not want us to move in together, I want to take the time for each of us to establish our own independent households & I want to make our courtship special, not everyday ordinary. I want to take the time to grow as individuals and then to grow together in hope we are stronger and better in the long run.
I think honesty is good. “We are both going to be going through a lot of changes as we go from being a students to launching our careers. We both need and deserve the space to grow individually so we can bring more to our relationship and so we can build a stronger future.”
My parents won’t let me. 
You need to view this as an extremely serious commitment. If there is any doubt that this is not the person you want to have a long term relationship with, then now is the time to start extricating yourselves, or at least not get in any deeper… I had friends that did this. High school sweethearts, they stayed together through college. I thought they would be the first couple in our little group to get married. After graduation, they lived together for about a year I guess. Then he announced he had met somebody else. This new girl was almost the opposite of his girlfriend. So, I think he must have had some doubts somewhere along the way.
This could work if the parents have to co-sign the young person’s lease.
I’m not sure whether it’s convincing otherwise since the parents are no longer in control of a post-college kid’s lifestyle.
When my kids were in high school, they had total freedom to use “My parents won’t let me” as an excuse for anything they wanted, and I said I would back them up if they needed to use it. I suppose it could also have worked under some circumstances in college (for example, to back out of a spring break trip without hurting people’s feelings). But it doesn’t seem to be as useful for a college graduate.
I don’t view it that way. Logistically, breaking up with an SO that you’re living with is no worse than breaking a lease if you have a roommate. It’s a much lesser degree of commitment than an engagement (which quickly evolves into giving large deposits to wedding vendors), a marriage (which requires legal action to dissolve), or having a child together (which is irrevocable).
Admittedly, if you’re living with your SO, you can’t just sort of drift out of the relationship the way you could if you lived separately. But breaking up is not the end of the world.
I wouldn’t expect my kids to use my disapproval as a shield in a discussion about their relationship. OP needs to own his reasons, and be honest with her. If he can’t be honest about this, either because he doesn’t want to or she can’t accept it and compromise with him, it does not bode well for their relationship long term. This is why people say relationships are hard work, OP.
Is this better (i.e., make you look more like a mature, responsible person who cares about the relation, less like an immature, dependent person who has not grown up, that is, less like Momma’s boy or Daddy’s girl.)
“I want to get on your parents’ good side.”
This assumes that the parents of GF or BF happen to be like the majority of the CC parents here.
This assumes that the parents of the GF or BF realize that at least one member of the couple has reservations about living together immediately. Many of us here wouldn’t object to the couple living together if both were sure it was what they wanted. Some parents of young women might even prefer that they live together (mostly for safety reasons – she wouldn’t be coming home alone from the BF’s place late at night, for example).