Hi op, so first off, good on you for supporting him, doesn't always happen!
So first off, this is quite a hard question to answer, as we don't know you or your situation, but first off, are you tied to one location due to your career?
I have to say long distance can be quite strenuous, but if your willing to make it work it can also make relationships much stronger, especially as it keeps things fresh.
I would say don't think about the initial part with him in training, this time flies and it's important for him to just get on with it. Afterwards, then there's so much support and having him in a stable career helps massively when planning for the future