My boyfriend get angry and upset about things

Me 25 and my boyfriend 30
My boyfriend has a stressful job snf life, so we have tried to make s commitment that our time together is too precious to be spent arguing.
Because if this stress he doesn’t like to talk about things that make him upset, stretching to our relationship. This makes it difficult to navigate as because he doesn’t talk to me about why he’s upset, I don’t know to not bring up certain topics etc.
moreover I feel like it hurts me knowing he’s sad so I try to ask what’s wrong and he gets upset with me when I try and talk to him about it because he’s said he doesn’t want to talk- which I understand but a lot of our fights are things that if we talked about them, it wouldn’t have ever been sn issue.
Moreover at the beginning of the relationship, before gf and bf, he was very open about his previous relationships, which set a boundary to me that it was ok about me talking about mine.
He didn’t like that I did that, I apologised and explained, yet he still brings it up now ‘saying he knows more than he wants to’ and is struggling to get over it.
Bear in mind I don’t think anyone’s past relationships should be an issue in the present, but when I tell u I’m very much s prude with sex etc so I feel like he is overreacting z
It makes me irritated that he struggles to get over my past when it’s nothing compared to his, again it’s not anything shameful, but he had had quite a few one night stands and been in way more sexual relationships than me.
I find it irritating that he doesn’t see that I’ve also had to put up with a lot and made a conscious choice to get over it because I think our relationship is more important, all the while it still bothers him.
Advice

if he’s stressed about something that is out of your relationship like work for example you should accept that he doesn’t want to talk about it however if it’s something in the relationship that causes his stress then accept the fact that he doesn’t want to talk about it right now but he should address it after. This is how communication should work especially since this man is 30 years old he should be capable of doing this. I know it hurts to not fix the matter as soon as you detect he’s upset but sometimes it’s best if they don’t speak about it at given moment since they want to gather their thoughts or relax their mind before a proper conversation. You should convey to your bf how you feel and tell him how it’s unfair on you to be left in the dark about how he’s feeling but how you respect his feelings to give him space when he needs it.
With the previous exs thing, i think it’s just his immaturity at this point but it might be unresolved issues with what you said, this needs to be discussed maybe something irked him about what you said even if it was little. Reassure you love him and communicate with him about it. If he refuses to talk to you about it at the given moment give him space tell him you should discuss it later as it’s important. If he refuses to speak to you about it at all, it’s selfish that he wants to hangs this over you without actually solving the situation. It’s a manipulation tactic to make you feel bad