Sex is getting boring

I could really use some advice 😕 I feel like a terrible girlfriend. My boyfriend of two years is really wanting to spice up our sex life and I feel so embarrassed talking about it. Background-was with my ex for 3 years it took a lot for me to get comfortable to do fun, different things with sex and he completely ruined it for me started cheating, saying I wasn’t hot enough, forcing himself on me whenever he wanted something etc. My self esteem took a huge hit and I’ve just never been comfortable talking about it since (I think worry that it may happen again even though I know my boyfriend is not like him). Now I’d like to start doing new things but idk how to talk openly about these things anymore it gives me bad anxiety and make me really sad like I’m failing him as a gf. He expressed to me some of his fantasies (like a threesome, I told him I am not comfortable with it and it seemed to upset him..). I just don’t know how to talk about this openly and where to start. I also don’t always feel confident with my body so that I feel takes a toll on our sex life.