Therapy!! I know it’s always thrown at people here as a suggestion but it’s for good reason. A safe space to talk about these things, to get to the root of it and work on how you see yourself will do wonders.
Also, depending on how comfortable you are and how sincere this guy is, maybe it would be helpful to open up to him about past experiences? A good human will tell you that there’s no rush, no pressure, no judgement and that at any moment you’re uncomfortable then you can try again another time.
Any time my partner has given me reassurance in moments of vulnerability it’s almost made me more excited because of how safe he makes me feel and unwinds the issue in my head because I realize no matter what, he’s with me no matter how that looks.