I've been dating my boyfriend for some months now, I think it's time to get intimate, I DO want to, he's not pressuring me or anything, he only brought it up once to say he was okay with my boundaries, but I'm still scared,

I've only had ONE mildly positive sex experience, I try to initiate (because he won't because when he did i was uncomfortable and he stopped), but I just feel so anxious because of previous experiences (one guy tried to do anal without telling me, right after taking off his condom, which I also didn't consent to, my ex pressuring me all the time, my ex bragging about having my pictures, my ex silent treating me after having sex, etc).

Now, I can't tell him this can I?, it'll be like telling him that I'm a doormat, I've also dealt with all that already, I don't want to relive trauma, I'm not the same person anymore and I'm embarrassed I let all that happen

I can't find the words to tell him that I want to go slow and that I might have to stop mid act if I don't feel well, because I want to be assertive whilst doing so but I'm just so soft spoken in person and don't want to look insecure. How can I achieve this?