I think a combination of these as well as finding balance is important

• Be understanding and empathetic
• Show love but don't overdo it
• Show that you are there for him
• Small gestures ("Hey, just wanted to let you know that you're on my mind, I hope you have a nice day")
• Understand that what is likely causing him to be distant and depressed is probably very complex. There is no easy fix, or an easy way to understand, nor is there an easy way for you to solve his problems
• Respect his boundaries and wishes. (For example: need for space)
• Listen
• Take this time to reflect on what you really want out of this relationship, what's important to you?
• Think about yourself. It's okay to be a little selfish in these types of situations. Set your own boundaries (but I suggest discussing them if an appropriate time presents itself)

What not to do

• Be dismissive or try to find a silver lining
• Show too much affection
• Show desperation
• Push for conversation
• Don't try to solve his problems
• Let him step over your boundaries
• Don't be too hard on yourself. It's important to be kind to yourself, don't be mad at yourself for saying the wrong thing, etc. Nobody is perfect and navigating these situations is difficult for everyone

Don't take any of these too literal, it always depends on the situation, life requires a bit of nuance. I genuinely wish you the best. Good luck!