Propagation is one purpose of sex (Gen. 1:27-28; 9:1). That doesn’t mean it is the only purpose, nor that there always has to be the chance of pregnancy. Birth control is an option for Christians. Such things as abortion or infanticide (Lev. 18:21; 20:2) are strictly out, though. Personally I don’t feel right about sterilization (Dt. 23:1l Lev 21:20; 22:24) but I don’t think that is a Biblical absolute. Just remember that conception is a GIFT from God (Gen. 4:1,13; 16:2; 17:19; 29:31; 30:22) and children are a blessing/reward from God (Psalm 127).
Pleasure is the other reason for sex. Unlike animals, sex for humans is “pleasure with a purpose.” People continue to have sex after procreation is possible. There is a pleasure element added that animals don’t have. God created sex to promote mutual love (“one flesh”). God told Eve He would give her a physical desire for her husband strong enough to overcome the anticipation of labor and birth (Gen. 3:16). Isaac “caressed” his wife Rebekah (Gen 26:8) in a way that made Abimelech discover she was not his sister. The Bible often speaks of the joys of married love (Prov. 5:15-19; Song of Solomon 7:6-10).