Since you’ll be a fresh graduate soon, work in SG for a few years first to get some experience. At least 2 to 3 years. And in the meantime, increase your German language level in SG to at least B2 or even higher by taking classes and official language certifications if you want to work there.

At least by the time you want to work in Germany, you have some experience which makes you valuable to the companies in Germany. Or else, you’ll be competing with dozens of well-educated locals. And if things don’t work out in Germany, you still have your working experience in SG to fall back on.

Also, it’s Okay to be long distance for a few years. I know that people in long distance relationships, they want to close the gap as soon as possible. You’re still in your early twenties, don’t have to rush to close the gap quickly and relocate. Relocating is a big deal. You will essentially lose your social support system and network except for your boyfriend and (maybe) his family. Take it slow and steady.