Present Tense

This is a matter of expression.

"I always love you." is a statment of facts. (The example you've used regarding the sun rising is this kind of facts that a person you have no control of.)

"I will always love you." is a promise. (This is not a statement of facts using present tense with an "always", where the "always" is an expression to indicate the relative time duration for the action "love". Using "will" has the meaning "from now forward". The person can take control of what he/she says.)

When you ask this question based on the "always" as an indicator for a "usual factual occurance", this is only basic grammar. Please take note it is only an "indicator", not a "must" rule. In real life, "always" does not always mean using present tense.

"We will always be friends." or "We will be friends always" is also an expression used by native English speakers - which is a good wish or promise, not like the equivalent Chinese phrase 友誼永固 - sounded like a factual statement with a subtle unlying wishful thought.

ALWAYS

1. frequency:
always = at all times (with the present simple)

I always love my Dad.
That means I love my Dad all the time. (in the past, now and in the future)
We often use present simple to state truths and to describe things which we feel are facts.

2. Length of time:
always = for all time in the future

You and I will always be friends.
I have known you only for a month. You stress more on the future and "always " connotes a sense of “for ever”.

In speech, we stress "will" to indicate determination, especially when the determination is strengthened at the time of speaking.

The Christians say “Jesus always loves you.” ~ past, present, future

They don’t say “Jesus will always love you.” because it implies that Jesus might not love you in the past. If they say that, they are not so sure about the past.