Should I end things?

I am 29(F) and my boyfriend is 28(M). We have been together for almost 6 years and have lived together for about 3 years now. We are high school sweethearts that broke up for college and reconnected. When we initially began reconnecting, we were living in different states and I was still with my ex. So essentially, I was cheating on my ex with him. Eventually, I moved back home so we can be closer to one another and we have been together ever since.

Our relationship has not been smooth sailing. We both are the type of people who like to be right and that has gotten us into some nasty arguments. However, overtime I have learned to just let things go and he just wants to bicker. Since the beginning of our relationship, I have made it clear that I do not like the way we communicate. He has done little to nothing to fix that. He continued to gaslight and yell during arguments. Also, he is a gamer and sometimes I feel like the video game is more important to him than I am. It has caused many arguments and leaves me feeling lonely quite a bit. Lastly, I sometimes feel like it is difficult to connect with him because he is not comfortable with emotions and vulnerability. I crave deepness and closeness with someone and I feel like it just makes him uncomfortable. This lack of deep intimacy has made sex awkward and difficult to initiate and when I go out with friends, I find myself flirting with other guys and pushing the boundaries because I feel so desperate to gain that emotional closeness with the opposite sex. I have even considered going on dates with other people.

He is a really great guy in other ways. He is responsible, driven, kind to me, protective, loyal, and I know he loves me deeply. I love him deeply and I care about him a lot but it seems the next steps for us are marriage and I feel terrified to take that step with so many doubts. I have suggested couples therapy but he seems extremely hesitant given the fact that he is incredibly uncomfortable with vulnerability. I am feeling so scared to end things because I am scared of hurting him or regretting my decision. But I do not want to get married and get divorced. I don’t know if I am being ungrateful of my situation or am I justified in feeling like something is missing. I need an outside perspective.

TL;DR: After 6 years of dating, marriage is looming. I have many doubts because of the lack of vulnerability and intimacy in our relationship. He is a great guy in other ways but sometimes it feels things are missing. How can I move forward?