German Language - Terms of affection / endearment

I know there are some wonderful native German speakers around AW. Can I pick your brains?

My German is extremely basic conversational, and I'm having a devil of a time trying to find just the right word for this situation. What I have is a present-day, early 20s German living in London. He is a gender-normative, masculine young man who is openly and comfortably bisexual, and I need an appropriate German term of endearment that he would use affectionately to a male lover.

He wouldn't say anything that was notably colloquial to queer culture, or anything that sounded old-fashioned, so it has to be contemporary and more or less gender-interchangable. For reference, his English partner calls him "babe", and he somewhat playfully uses this term in response.

Any suggestions warmly welcomed. Danke.

Thanks everyone. Interesting to hear Schatzi mentioned a few times, I had considered that but resisted because of a perception that it was a bit fuddy-duddy. If it's more common among younger generations, that may not be as much of an impediment as I thought.

I do like the sound of Junge because of parallelisms with colloquial English "lad", and I didn't know it could be used for endearment. Thanks for that, I'll give it a ponder for a bit.

For that matter, I stumbled across "Bube" as a southern German term for a young man that might be roughly comparable to 'lad'. Anyone able to say if that would be a wholly peculiar word to use as a term of endearment? Punning on babe/bube could be fun in dialogue.

Hah. That's a good point on "booby", Taiga. Thanks for that. That could be fun in another context, but it wouldn't work for these guys!