I [23F] have been with my boyfriend [25M] for 8 months but he wanted a "break" halfway through. I have been insecure ever since and I often fear that another break or breaking up will happen again. What can I do?

Prior to relationship: We have been close friends for 7 years. We were part of the same friend group, but always gravitated towards each other, had horrible sexual tension, spent all night talking after everyone fell asleep at parties, shared our deepest thoughts/feelings, took care of each other while sick, etc.
We went to separate colleges, during which time I had a LTR and he had tinder hook-ups. We saw each other several times a year during gatherings with mutual friends and the interactions were painful for both of us.

Beginning of relationship: 2 years after college we start talking more because he wanted my input on a project. One thing lead to another and he told me that he's always loved me, and that he feels like he is on the brink of greatness with his career and wants someone to share his life with. He knew I was traveling around at the time anyways and he wanted me to come to his city to be with him. I was very cautious at first and we talked about it for about two months. He agreed to discuss life goals/compatibility before I decided to move. Then we went into the honeymoon phase HARD. Sex multiple times a day, within 3 months he talked about living together and I talked about plans for us years in advance. We were spending every waking moment together and he started paying less attention to himself/work. I enabled it...

The break: 4 months in he got stressed out about his life and wants a break from our relationship. He's stressed about 1) not feeling accomplished in his career, 2) pressure from his peers to be a single, 3) the relationship going too fast, 4) fear that being in a LTR could jeopardize his success, and 5) never having casual sex (I found out at the beginning of our relationship that his tinder hook-ups were only blow jobs, and deep seeded Christian guilt prevented him from having sex with them. I am his first, but he is my second.)

He was worried about being "basically engaged" at 25, and was worried he wouldn't progress in his career, or live out what every man should experience (incl. casual sex). But he also said that he loved me more than he had ever loved anyone and didn't want to lose me.

He wanted an indefinite break to figure out what he wanted. I freaked out at first and said I would rather him break up with me than go on a break, because I couldn't handle the uncertainty. I eventually agreed to the break after some convincing. However, I expressed that I would not actively try to find someone else but that could not wait on him forever. The break lasted 3 days and he said it was the worst 3 days of his life. I still worry that his decision to be with me was out of fear of losing me and not because he was actually ready to be in a LTR.

Relationship now and insecurity: He figured out how to balance his work life and personal life, and is doing much better. 1) He has had more achievements at work, although he is striving for much, much more. 2) He has made peace with his friends wanting him to be single, and many of them have actually entered LTRs as well.

I started staying with him in March because I was being exposed to the COVID through my job but lived with someone who was especially vulnerable. It was meant to only be for a few weeks, but it turned into months. Once this blows over we may go back to living separately, but he has expressed desire to continue living together, finances allowing. We've stopped talking about making definite plans about our relationship in the far future, but still discuss things hypothetically. I'm not sure if this is still moving too fast for us (3).

However, (4) I think he is still worried that being in a LTR hinders him. He never changed his social media status to "in a relationship" and when I asked why said that for business it doesn't look good to be in a LTR because those guys are seen as less ambitious and more "comfy". He is very open about his intentions to be with me to all of his friends and family, but he doesn't want the general public to know I guess. I haven't brought it up since, but it makes me sad.

For his concern about never getting casual sex (5) he's asked for threesomes or a hall pass, especially to be with younger/petite women, as a compromise. I initially had a hard no but he was very annoyed, as he was aware that I was open to the idea when in my previous LTR and thought I would be okay with it. He says that he would never risk losing me forever in the name of casual sex, but he still brings it up (ex: telling me he had a dreamabout wanting to have a threesome, but not going through with it and being frustrated).

Right now he's gone on a business trip for 2 weeks and I'm dying of insecurity that he will be tempted to leave me by some huge career opportunity that takes him across the world or by seeing his coworkers bingeing on the local women. I'm worried his desire for these things will outweigh his desire for me.

I've been pretty open about my insecurity ever since the break (I can't function keeping things from him), and his words were only supportive. He says that being with me makes him a stronger man and therefore betters his career. He also said he is making the conscious decision to potentially sacrifice casual sex to have me (although he still thinks I may change my mind about threesomes).

TLDR: My boyfriend wanted a "break" because he wanted space to figure out if he's willing to sacrifice absolute freedom in career pursuits (like on-the-spot business trips for months) and casual sex for a LTR and eventually family with me. We got back together and he has tried to reassure me, but I feel like only half of the problem has been solved. I have terrible insecurity about the break and fear he will leave me.

What can I do? I want to stay with him, but how do I get over this insecurity?

So far I have:

  • Boosted his confidence in every way possible about his career whenever he has doubts
  • Doing my best to boost our sex life
    He's asked me to wear outfits (characteristic of teenagers) and I was uncomfortable at first but was able to get into it. Partially out of genuine desire, partially out of hopes that it would maybe satisfy him about threesomes/hall passes with younger women.
  • Refrained from intiating any conversations about commitment and long term plans to avoid putting pressure on him
  • Expressed willingness to be flexible to his career needs.
    I wanted to go to graduate school next fall, which would either force us into a long distance relationship or restrict him on location. I would be willing to drop it all and move around with him if he could support us, and I think he knows that and wants to do that, but he isn't at the point where he can guarantee a lifetime of financial security.
  • Stayed firm on my discomfort with him having casual sex with others with or without me present.

I know at the end of the day I can't change him or his desires. He says he wants me but I feel like my trust is broken and the fear of losing him is destroying me. I'm worried we got into this relationship before either of us were fully realized individuals and now we're struggling to balance personal growth and relationship maintenance. Thanks for reading. All of my friends despise the RPW mindset and I'm lost.