Ya can't make up your mind to trust someone, or be vulnerable with 'em. Vulnerability comes thru learning another is trust-worthy, and having enough history together that's proven you can RELY on it.
I had a young male client many years ago, who stated he was "trying to be vulnerable" with the woman he was dating. Anyone who asks you to be open or vulnerable with 'em, has no fucking idea about genuine intimacy, and what it takes to BUIILD it!
Trust is a FEELING in one's inner core~ not an idea or concept manufactured in one's mind. You can't MAKE someone trust you, any more than you can make 'em love, admire or respect you. All these characteristics must be earned, over a considerable amount of time~ which makes the notion of "love at first sight," utterly absurd.
Men are notorious for getting trapped by Borderline Personality Disordered women who first pathologize, then NAG 'em about "opening up and sharing" what they're feeling or thinking, LONG before emotional trust in the relationship can be cultivated.
This is a serious lack of boundaries and empathy that people with BPD traits are well-known for, incidentally. The Psychologically Naive presume there's something "wrong" with themselves, if they don't feel comfortable shedding their self-protective defenses with someone they barely know . . . and there's the rub!
Borderlines (both male and female) are spectacularly adept at making you feel guilty, ashamed, unworthy of their affection, etc. This always happens after they've seduced you into entertaining fantasies of "happily ever after," because they've love-bombed ya almost from the start of your romance, and it's hard to even imagine, the euphoria you're feeling has an abbreviated lifespan!
So many wanna "fall in love," due to the out-of-control, intense emotions that are triggered during a new romance. Yet, don't people spend the rest of their days trying to REGAIN the sense of balance, order and control they chose to abandon at the start of that relationship?? Of course they do, silly!
We GROW to respect someone. We GROW to admire them. We GROW into loving them~ and with any luck, trusting 'em, if they've earned it from us!
It's virtually impossible to love someone ya can't trust or respect. Only fools think otherwise.