What does this mean? I just want to let you know that I love you. I'm so sorry that I have not been the person that gives you what you deserve.
It sounds like he feels that he just can't, at the end of the day, please you.
There are a number of possibilities here:
He's doing everything he can, and it's not enough for you.
He's doing everything he can, and he thinks it's not enough for you.
He's invested what he's willing to, and it's not enough for you.
He's invested what he's willing to, and he thinks it's not enough for you.
He's feeling guilty about something, and he's not willing to come clean.
He doesn't really love you.
Or to put it another way:
He's lying to you or himself.
You're lying to yourself or him.
You're both lying to yourselves or each other.
So what's to do is check in. Do you want this, really? If it's a yes, does he, really, still want this? If either of those is a no, get it complete, move on.
If you are both still clear you want a future together, I'm guessing either he has issues about whether he is good enough for you, in which case this might help, or you are leaving him guessing, or somehow constantly demanding that he prove his love, in which case it's up to you to take responsibility for it, and create a new future with him.