Advice? Dealing with the past.

So my bf and I been together for almost a year and a half. When we got together he was going thru his hardest time of his life so far. His mom had cancer and she pasted away a year ago. My bf is only 21 so I can’t imagine losing my mom (I’m 21 also). So anyways when his mom passed away things in our relationship changed. I felt that he would take his anger out on me he never abused me or anything of that sort. Things between us did get really toxic so we decided to end things while we were still on good terms. Long story short about a month after we broke up we got back together. He promised things will be different. Which they are he’s a completely different bf. I love our relationship now. He so loving and caring and I love everything about him. Time has passed and I thought I got over the past but sometimes when I’m up at night I find myself thinking. Thinking about him, thinking about our past and how shity our relationship was. Then I get all sad. Then I start to over think. Then I get mad because I don’t want to think about the past. because my bf isn’t the person he was. I don’t blame him he lost his best friend(his mom) so I get it. Things were hard for him at the time. Idk how I’ll act if I went thru what he went thru. I’m just venting. I love my bf he’s my best friend and I hate that I keep having this negative thoughts. I hardly don’t ever think about the past but when I do it hurts.

What can I do?

Thank you so much if u read this ❤️