My girlfriend (22F) broke up with me (21M) because of my confusing sexuality

I am a 21 yr old male, and have identified as straight my whole life. I’ve never had romantic thoughts about men, checked out men in public, or anything like that. The thought of kissing a man or doing anything intimate makes me feel gross- But I’ve always been attracted to penises and crave trans porn and sometimes gay porn if it doesn’t show any faces. I know this is weird. Since I was young I’ve liked girls with short hair and boyish faces, and in the past few years have had lots of fantasies about sex with trans women. I still identify as straight though because I couldn’t see myself actually acting on these fantasies. My girlfriend of 8 months has always been insecure about me talking to other women, liking their pictures etc, so I haven’t been open with this side of my sexuality because I knew it would lead to even more insecurity as her first boyfriend ended up being gay. She broke up with me about a week ago because I admitted I think about dick, and she feels like I’m a liar because I say I’m straight. We are having intense fights every day because she feels inadequate, and like I want something she doesn’t have. How do I get it across to her that satisfies me and has nothing to worry about? How do I save this relationship? Currently writing this while crying in my work bathroom so sorry for any confusion.

TLDR; Girlfriend broke up with me because I think about dick sometimes and she has insecurities from past relationships.