Nature or nurture. It’s always hard to know from a letter whether a person is suffering from a biological problem or from the result of experiences. In most cases, it’s a little of both. That’s probably also true for you.
Let’s start with biology: It may be that you have a low-grade depression called dysthymia. Long-term feelings of worthlessness, sadness, and generally being down are hallmarks of this disorder. Sometimes it moves into depression. In terms of experiences: You had a traumatic experience and then apparently were so well taken care of that you didn’t learn to take care of yourself. The two may well be interrelated.
Fortunately, whatever the reason, there is something you can do about this. First, if you haven’t had a physical exam for a year or so, you should see a doctor to make sure that there is nothing medically amiss that is contributing to your feelings of apathy and depression. At the same time, make an appointment with a psychologist or counselor to get an evaluation and to start some therapy. In therapy, you will have the opportunity to finish any recovery work you may need to do from the past. You will also have the support you need to learn to be more assertive and self-confident.
At some point, you might want to consider some group therapy. Group treatment will give you a place to try out those new skills with the added support of coaching and feedback from the group leader and members of the group.
You are still young so patterns aren’t so entrenched that you can’t change them. You made an important first step in writing here. I hope both the love of your partner and your desire to be a better partner for him will help you stay motivated. It will be hard at times but I have a strong feeling that you can get there.
I wish you well.