Repost because I put in the wrong flair.

Hi, this is pretty much a throwaway account and I am desperately begging for advice here
I’m gonna give some context to this so bare with me

So me and my boyfriend have been together for six years totally.

Two years ago (back in 2018) my boyfriend (24 is his current age) cheated on me (20 Is my current age) It was a one time thing with a girl at a concert, he never told me about it and I found it out on my own. We decided to rebuild our relationship after this, and to communicate properly about the issue. His excuse was that he felt bad for me, since we were both going through a depressive episode. I was basically his caretaker at the time, such as cleaning, cooking for him since he had no energy to, the list goes on. He felt so guilty about it that he chose to cheat, so he would have a reason to break up with me without feeling bad about it. He then ended up regretting it so much that he never told me. 
He has always been very understanding of my emotions and overthinking after the whole thing. 

So, now he will be gone on a business trip for two days. When he first told me a month ago, I immediately jumped to the worst conclusion possible. We’ve barely talked about it until yesterday when he was packing his suitcase.
I started crying really badly, and we communicated about it until I eventually calmed down. However, today when he left, I’ve been feeling like complete and utter shit.
We texted a little bit just now, and his day has been going well so far. I managed to stop overthinking (or so I thought) when I reminded myself that he has been very open and honest about his emotions through the whole cheating thing, and has given me a lot of reassurance. He has for a while been talking about wanting to marry me. When the marriage thought hit me, I stopped being nervous and it just brought me some comfort. Surely he wouldn’t bring up something as big as marriage unless he really loved me and wouldn’t leave me, right?
They will be served dinner soon and after that there is a social gathering for them. I am now spiraling, I feel like I’m going to vomit, my chest hurts and I want to kill myself. I’m scared he’ll fuck someone at the trip and never tell me about it. I’m scared he’ll be laying in bed with another woman and I am seriously thinking about killing myself so I won’t have to deal with the pain of being cheated on again. And I cannot reach out to him about this (or anyone else) because my feelings are not his responsibility.

Thank you if you read all that. I’d love some advice right now, or just someone who wants to listen to me being a dumb child.