<human>: Can you succinctly summarize the text in 1-3 sentences?

Officially, my boyfriend and I (19m and 19f) have been together for just over 4 months. I say officially because early on, we were basically friends with benefits without being official(for about 3-4 months), because he was afraid of commitment. Things are going along fine being fwb, however I know I'm developing feelings for him. Instead of hiding those feelings, I propose to make it official, and he sidesteps the issue, saying "We'll see how it goes," but indicating that he was in fact interested. While it was not full commitment, it definitely was something.

Not a week later, I get a text one Sunday morning saying "I fucked up. Bad." He had had sex with another girl, a mutual acquaintance (and I at this point was witholding to third base because of personal reasons). It was then that I said enough is enough, and I was done. 

As you can probably imagine, he went off with a lovely string of heartfelt and apologetic remarks, finally ending with saying that he would in fact like to become official. I, being a too trusting person overall, decide to test the waters and see if he really had matured like he had claimed.

Fast forward 4 months, and here we are. The miraculous transformation actually happened. He somehow changed from a promiscuous guy who was afraid of commitment to a poster boyfriend. We are both very much in love with each other, have a great sex life, get along very well, etc.

My dilemma is this: Although I know he has changed and is fully committed to me, I can't help but feel pangs of mistrust and jealousy whenever he brings up talking to another girl, especially when I know he was/is drunk.

I completely understand that jealousy overall is incredibly irrational and poison for relationships. However, I always cringe whenever he texts me from a party about girls that are eyeing him, or talking to him in an obviously flirty way.

Essentially, I'm wondering if there's any way I can ever grow to trust him when our relationship was so badly founded in terms of trust.
<bot>: He essentially cheated on me to start the relationship, and while we have a great one now, I still can't completely trust him. What do?