For your boyfriend's birthday, you can give him a customized 925 men's silver necklace. It is customized and can be engraved for free. There is only one in the world. It is a very personalized gift. Your boyfriend will treasure it well. You can also give him a couple's necklace, one for each of you, which means that your love will go further. Even if he is abroad, you should send your blessings to him and don't let him feel lonely. You should bless him as if you are with him when you are not with him.
If you can customize a cake for him as a birthday gift, I believe he will be very surprised, but more of it is still touching. You can ask the cake shop near your boyfriend and ask them to make a cake for him on his birthday and write a blessing card. I believe he will be very touched.
I saw that there are customized handmade chocolates on the Internet, which feels pretty good. You can also write blessings on the chocolates. It feels very thoughtful. Give one to your boyfriend.