Why Do I Pull Away From My BF

This is my first ever post and I don’t really know how this works but I need help so I’ll get to the point.

I(18f) have been trying to have sex with my Bf(18) for a while and our inability to do so is causing a rift between us. Everything else in our relationship is great but our sex life. The foreplay is amazing and I usually enjoy it but its the penetration that is the problem.

We try find our groove and take it slow but it never works. It feels great but it gets uncomfortable and it feels like alarm bells are going off in my head and I should pull away but I don’t want to but my body is just rejecting the pleasure if that makes sense.

I really want to enjoy sex especially with the man I love so if you have some advice for me to get this mental block to stop I’d really apricate it so much.