Your boyfriend is doing what he can to reassure you. He loves you and your body, even though you don’t. He hasn’t done anything to make you question whether he is telling the truth. His former partners know he chose you over all of them. Rather than celebrate that, you focus on his history as a negative. It makes sense to me that you feel so “crazy”. This is such a hard way to live.
As you suggested, your problem is one of self-esteem and insecurities coupled with a mental health disorder, Body Dysmorphic Disorder (BDD). Without knowing more, I can only guess that this is a major contributing factor to how you are feeling.
Body Dysmorphic Disorder (BDD) is characterized by irrational focus on perceived personal physical flaws or defects. Contributing causes for BDD are low self-esteem, perfectionism and competition with others. Often people with BDD are preoccupied with their perceived physical defects and constantly compare themselves unfavorably with others who they believe are physically more attractive. That sounds like you, doesn’t it?
The good news is that BDD does respond to a combination of Cognitive Behavioral Therapy and medication. Although there is no medication that “cures” BDD, selective serotonin reuptake inhibitors (SSRIs) have been found to be helpful in many cases. CBT will help you challenge the negative thoughts you have about your body and stop making negative comparisons with others. You will learn new ways to manage your impulses and to cope with negative thoughts and feelings.
If you are not currently in the care of a therapist, I urge you to make an appointment — now. If you have to wait for an appointment, you can make a good start by working your way through one of the CBT and Body Dysmorphic workbooks that is available from booksellers.
You are only in your 20s. Treatment now will prevent years of feeling inferior and distressed. I do think that without treatment, you risk losing the love of your life.
I wish you well.