No, it's not totally true - Or at least he doesn't know.
He might meet someone else tomorrow and forget these words - 20 years from now, he might love you and love other women as well - Love is often NOT exclusive and people might end up loving more than one person.
The point is the "I will love your forever" expression is a romantic statement that is expressed when we are in this romantic, passionate and in love state.
But this state is not permanent.
When reality hits you and you are confronted with the others aspects of life like job, money, and other practicalities, this romantic reality can fade away...
Sometimes, a man will say "I will always love you" and then break up with you or marry someone else, right?
So, what about his new partner?
Is she just a joke or what?
In a moment of intimacy, he might say the exact same words to her.
What about men who have been married 2 or more times?
How many times did they repeat the same promise and same type of vows.
They will say things like "For better or for worse", "I will always be at your side", "You are my only lover and best friend", etc.
A few months or years down the line, what do these words mean when you are fighting a divorce battle?
See how it works?
There is the romantic dream on one side and then there is REALITY!
No need to kill the romantic dream of course.
You can still totally enjoy these romantic conversations but stay REAL.
...And when a man tells you that he will always love you, enjoy these words, enjoy their beauty and keep in mind as well that this romantic dream might have a high degree of impermanence.