Sex is uncomfortable

So I wasn’t super attracted to my ex but I could still get wet enough for penetration. However, sex would usually feel uncomfortable if he wasn’t constantly on my clit and I’d dry up. He used a bit above average in length and when he tried to completely enter it’d hurt or he deeply uncomfortable. It was so bad cowgirl wasn’t a possibility. I’m nervous with being someone else after how it was with him. Was it me or him, please give me any advice you could provide x