Marcela,
Hi there. Welcome to BPD family.
I'd like to caution you about focusing on a need or desire to tell him he has BPD, here' read a book about it, for a few reasons.
The biggest reason is this" BPD is not like depression or bipolar disorder, or other mental illnesses and conditions that can remedies sometimes with fixing a chemical imbalance in the body. It's a behavioral/emotional disability, that is highlighted a lot of times by blame/shame avoidance, and fears of abandonment.
This about that for a minute. If you have a condition that makes you pathologically start fights, be unpleasant and irrational to avoid blame in any situation, often about things that aren't even a big deal, how would you handle the person closest to you telling you that YOU are to BLAME for problems in your life and you need to fix yourself and read a book about it?
You'd engage in mental gymnastics and cause a fight to prevent seeing that you are partial to blame for the drama in your life. You'd project your BPD onto the person telling you YOU have BPD. You'd say/do anything to avoid being the cause of any of the strife and to avoid the shame that would come with accepting the blame.
We all come here with a Eureka! moment. we've found what is going on, and tools to help deal with it, and people who won't just dismiss us as crazy. There's a term for the cause of drama at home, and we're excited to see a light at the end of the tunnel, and we think, "ok, it's just like telling him he has diabetes, and he'll see the light and want to work on himself." Except, that is the total opposite of pretty much what anyone with BPD thinks.
This is a process. Your lives can improve, and you can work on communicating more effectively in ways that don't trigger arguments. Arguments will happen - they are not BPD-exclusive. But they can be shorter and less often. Observe him, see what common triggers are over time, and how you can validate his feelings during those rough times so he knows you are his ally, not his enemy.
The biggest and really only thing you can do is work on you. Sadly, we do more to contribute to the fighting than we realize. we try to reason with an unreasonable person, and that just makes them madder, prolonging the fight, allowing them to fall deeper into the rabbit hole of BPD anger and irrational rage.
In page 331 they talk about us needing to state the Acceptance-Acknowledgement Declaration.
And as example "I never knew how much pain you were in. I never knew how much you suffered. I must have said and done so many things to hurt you because I did not understand or acknowledge your pain. I am so sorry. It was never my intention to cause you pain. What can we do now to improve our relationship"
My Q to you is: How can I do that? How can I tell him that he has an illness? It would be extremely great if I could make him even read the book (He is an extremely intelligent person), but how can I do that ?
I acknowledge that I have my part too (I am accepting and acknowledging) but it was just because I did not know about the (his) illness.
Now, I can start to work on saving my marriage. And I want to do that because I still love him and I know deep inside that he loves me too. So, it is worth
Page 331 says nothing about the statement being tied to a BPD revelation. Because it's not tied to it at all. You can tell him that any time it seems right, that you never realized his pain until you did some self-help work, and you're committed to working on how to better communicate. Done.
Then, work on listening to his FEELINGS about things. Validate the ones that are valid - it's a crummy day and he wanted to be outside, you can totally validate that and try to make him feel his feelings were heard. He says something off the wall or makes an unfair accusation, don't validate that. His version of reality is not what is validated, but his feelings about it.
Take a break, set a boundary about how long you will engage in an argument (this does not need to be a declared boundary, boundaries are often internal lines in the sand we place around ourselves to protect us from the drama) - one of the biggest things that prolongs an argument is our desire to explain the argument away. Instead of seeing that you've both reached a point where no discussion can be worthwhile, it's all turned into emotional word-vomit, and saying, "I'm not continuing this, I am taking a break until we can talk normally," and leaving the room, house, conversation however you can, we tend to try to say, "Yes I did that but if you'd only listen you'd not be mad." Read up on JADE - Justify, Argue, Defend, Explain - every single one of these actions is invalidating, and just keeps an argument fueled to keep burning.
You can mention BPD, but I have not, many members on here have not - it usually does a lot more harm than good, especially in the early stages of working on ourselves. Read up a bit on the tools, read more posts from others and you can get a better guge at how pwBPD react to certain things, and you can determine if it's a good idea or not.