Relationships.

I have anxiety, depression, show strong signs of a personality disorder according to my psychiatrist and I have awful trauma.

i'm a female, 18. My self-esteem in my relationship with my partner is bad. He is due to start going out with his piers/work colleagues for drinks and I need ways to keep myself calm and not have excessive stress about if i'm good enough. My partner has never cheated, flirted or done anything that could ever make me think twice about him, if anything he is the most trustworthy person i've ever met! But due to my past I think the worst of everything. We have both spoken about it. But I need advice elsewhere on coping with this.