1) Has your daughter (since she is his Girlfriend), asked him why he does not want a gift? She can ask him why, ya know.
2) Maybe he feels it is not necessary because you ALL spent on visiting him while he was in basic training.
3) How old is your daughter? Is she also in college? You said this is your daughter's "college boyfriend." So, is she in college with him too? Or not? Is she younger? The reason I ask is: typically, a college aged girl, can and does go traveling on her own or with friends. But... you/and your Husband, TOOK your daughter to go see her Boyfriend. With her. So... does that mean your daughter is not old enough to go see him, by herself????
And the other side of the coin is: the Boyfriend wants to see HER. And maybe he wants to see her... without her parents, there, too. Like a chaperone. Maybe he feels, hovered over. ??????
4) Or, maybe he does not want a Christmas gift, because he is going to break up with her. Or, maybe, she and you all.... are making him feel... a bit pressured.
5) Or maybe, he does not want a gift from you/your Husband, because HE cannot afford to get gifts for everyone. And he might feel bad if he does not get you/your Husband a gift. Too.
But for your daughter, since this is his Girlfriend, he may get her a gift.
Maybe, you/your Husband getting him a gift... makes him feel really obligated. And he can't afford it etc.
6) Then, they have been together for 15 months. That is not long. It is really up to your daughter and him, to decide how their relationship flows.
It may be a relationship that is long term and will progress... or, it is a relationship that is just, temporary. Not all relationships are "serious."
But that is your daughter's life. And choice. And between she and her Boyfriend.
7) Plus, the Boyfriend is far away. Did your daughter AND he, decide to continue the relationship???
Ultimately, this is your daughter's relationship.
And if the Boyfriend does not want a Christmas gift from you "all"... then at least he said so. But really, your daughter can ask him why. Since you... are wondering about it. She is his Girlfriend.
This is their relationship.