Boyfriend joining the Royal Marines

My Boyfriend is planning on joining the Royal Marines next year. He's already done his medical and was about to do his physical test before an injury, therefore deferring to joining next year giving us more time together. I'm 100% supportive of him and proud that he wants to do this but I'm just worried about how much I will miss him. Anyone out there got a partner that's in the Marines/ military? How do you cope when they are gone and how often do you see them/ speak to them? What was it like for the two of you to be apart? Any advice is much appreciated!