I can't have sex but I desperately want to

So over the years I've (23 F) had several partners that I have found extremely attractive and that I have genuinely cared for (I've been in love even)but for some reason when it came down to having sex with any of them I just couldn't bring myself to do it. My body seems to just lock up and I have this feeling like I want to crawl to a dark corner and hide and never come out .I keep wondering what the problem is because I can get off to the thought of them, I try to give them a good time in other ways but it seems impossible for my body to let it happen.

I have never been sexually assaulted so I have no clue why my body reacts like this. I had to leave my last partner (25M) who I genuinely loved because of the issue and I believe that they should be with someone who can take care of their needs. This issue is causing me a lot of heartbreak and I'm starting to question even my sexuality in all honesty. It's affecting my personal image and I'm really worried.