Thanks for your query.Based on what you have described it appears to me that your foreskin is not getting retracted freely on glans penis
on erection and so any attempt without foreskin being retracted completely to penetrate it into vagina results in tearing of the foreskin.
You have not mentioned about your age and whether you are diabetic or not.? Please get your blood sugar levels done to rule out the same
Consult some Urologist
or Surgeon for clinical examination.Looking at the the situation getting it repeatedly I would advise you to get circumcised to solve your problem permanently..