I didn't have sex at all with my second or last pregnancy and I didn't have any trouble with long labor or tearing. I believe it's all about relaxing. Remember if you are able to relax your jaw neck and shoulders your able to relax you perineum. I just had to talk myself throwing the pain and focus on allowing my body to do what it was created to do.
Also if u sit in warm water during delivery a bath or showerif possible massage there while in water itll help stretch you a bit
I don't think that will make much of a difference. You can help prevent tearing by putting petroleum jelly on your perineum (the skin between your vagina and anus), and massaging it, stretching it.