As a little bit of background, my partner (26M) and I (22F) are in a long distance relationship across the U.S. and we've seen each other several times since starting it about a year ago.

So, my partner has a tendency to not communicate to me when he's mad or upset at me about something. Let me set the stage and let me be very clear as well that this is the second time this has happened.

This is what made my partner go quiet. Two days ago, it was an online friend's birthday, so I made him a card with a doodle of a cake that said "Happy Birthday!" signed with my username because I thought it would be a nice surprise. I feel like guys don't always get compliments or have their birthday acknowledged, so I wanted to brighten his day in that respect. There are no feelings on my end. I told my partner about this. When I was sharing it with my partner, in my mind, I thought, "hey look, I'm trying to socialize and go out of my comfort zone more" which I was proud of because it shows that I'm trying to make friends - which I don't have a whole lot of anymore, since I've become wrapped up in my partner. That's not his fault, though.

Apparently my partner was fuming about this, but he didn't say anything to me. He just left me on read for a while and finally shared in some small talk texts before the end of the night, letting me know that he was going to get some sleep. He never goes to sleep that early but I wished him well anyway and tried to keep the mood cheerful because I wasn't sure what was going on, but I didn't want to jump on him either. I might have failed by not communicating my concern at that point.

What my partner tends to do whenever he goes quiet and short with me like that, is go onto a website that is notoriously known for having several sexual chat rooms. He then likes provocative photos of women (women posed seductively, bikini shots showing off the ass, etc) as a distraction from our conversation and has sometimes talked to them - even if it doesn't go anywhere. The last time he did this, it was because I went a little quiet and he started assuming that I was going to break up soon with him anyway (I wasn't, but he jumps the gun because he has a lot of relationship anxiety), and then he started making himself available to other women as a form of moving on from me. This is in his words.

I told him in the past that it made me deeply uncomfortable when he went into chatrooms like "sexy babes" (I'm paraphrasing) and liking photos of women "showing off the goods". It's one thing to look, and absolutely something else to act with intention. He agreed and promised me he wouldn't do that again. This happened over the spring. I kind of believed it but he relapsed and did it again tonight, so I became enraged and messaged him "why do you lie to me". He became confused and started panicking because I wouldn't pick up his calls, and eventually I answered after maybe 10 minutes and basically asked him why he was so quiet and eventually, why he was on that site again. I tried to be as level-headed as I could.

He said that he was jealous of the guy (24M) I made a birthday card for and that he sees it as a form of flirting. Then he came to the conclusion that I "must be cheating". I have never cheated on him and I was not flirting with the guy, but he explained how other guys might not see it that way, eventually I said that I understood, and that I would no longer make presents like that for men.

What he did is different. While he was on that site, he added one of his old friends, K (30F) And he also added a woman with the back of her legs facing the camera and her miniskirt almost riding up her butt - the profile was intended to be provocative. He was in several sketchy, sexual chat rooms as well. He told me that he and the provocative profile didn't talk that much and apparently "she was a lesbian". But what if she wasn't. And isn't he obviously looking for sexual attention if he's in sexual chat rooms?

My problem (and I told him this), apart from him breaking a huge promise and shattering some of my trust in him, is that suppose we have an uncomfortable period as a couple for a week where things are a bit tense and we aren't on great terms? This can happen in relationships. And in response, suppose he goes online, looking to other women for emotional support, liking their photos, starting to flirt because he thinks "that we're basically over, so what does it matter anyway"? That can lead to full on cheating. He assured me that he has eyes for nobody else and that nobody has made him feel the way that I do, but what happens if during one of his online validation stints, he does actually find a woman he likes, because he's opened himself up to this attention. Then suppose he starts developing the very feelings that he only used to feel for me.

So what do I do? He just promised again that he won't look online for attention from random women online, but he seems to have an addiction to it and I fully expect him to relapse - not because he wants to but because he has poor impulse control and always assumes that the relationship is going to end whenever things get tense. He doesn't work right now, either, and I'm worried that once he starts getting female attention there and we have a tense stint, he might start going to them for an emotional affair. And that's so much more dangerous than talking to women online. I've told him everything that I've said to you guys here except this last part, which I honestly might share with him.

I guess my question is, how do I work on trusting him and thinking positively again when there's a strong chance of him relapsing?

TLDR: Partner interacts with provocative women online whenever he's mad at me and doesn't communicate about that anger; I'm really struggling to trust him even though he says he do it again.