Sexually frustrated

My boyfriend of almost 2 months is in the marines and so our time is limited as it is, but on top of that when we do have time alone I ask him if we can have sex (virtually since we don’t live together) and he will usually say that he wants to but that he’s too tired from the marines and doesn’t want to fall asleep on me by accident. But it’s frustrating for me because when he finally says yes like tonight he ends up falling asleep anyway and I’m left sexually frustrates as hell. If anyone has any advice/tips or tricks please please please tell me! I’m begging you!