He only becomes competition if you choose to compete.
As for the trust-I do understand what you are saying.
In my case, my boyfriend has been my best friend for 20 years come April. He's been in the picture longer than my husband (we've been together 15 years). Furthermore, we have all lived together the last 10 years.
So there is a LOT of knowledge and understanding.
But-the bottom line for me is that some people aren't trustworthy for that type of role (advisor, confidante etc) REGARDLESS of if they are sex partners or not.
Other people are great for that-regardless of if they are sex partners.
If you don't trust HIM-that is a whole different issue to address.
If he's a gossip-that is a specific issue to address.
If you don't want your private info shared-that is an issue to address.
But each is different and ESPECIALLY in poly dynamics its IMPERATIVE to name the distinct and specific issue-not to allow ourselves to ball up the issues into being about "a lover" or "a friend" but specific people and specific behaviors.
Otherwise-we end up in a quagmire of semantical bullshit.
So-My advice is to sit down with yourself and make a list of what specific characteristics (not relationship status's) make a person a GOOD confidante and adviser. Then make a list of what makes someone not trustworthy as a confidante and adviser. Also make a list of what things you absolutely don't want discussed with ANY other people versus things that you are ok with being discussed with a trusted adviser/confidante, vs things you don't care who knows. Finally-what information is YOUR personal info, what is your partners personal info and what is "our" personal info. Because anything that is your partners and anything that falls into "our" is also your partners info.. where as things that fall under you alone-are not your partners to share ever-without your explicit permission.
Once you have that knocked out-then sit down with your partner and explain to them what you have written out and that you want to discuss with them creating an agreement of understanding regarding what information is shared and with whom.
(side note-I do grasp well what your complaint is-we had a doozy of a battle for the last year because my husband shared personal info with a new interest and she wasn't trustworthy and it did get used inappropriately-try to be calm and find a rational way to convey the info to your partner.)
"Love As Thou Wilt"