**To waste any seed is wrong. **
The Bible says:
**Genesis 38:9-10 **
9Onan knew that the offspring would not be his; so when he went in to his brother’s wife, **he wasted his seed on the ground **in order not to give offspring to his brother.
10But what he did was **displeasing in the sight of the LORD; so He took his life also. **
Deuteronomy 23
Persons Excluded from the Assembly
1"No one who is emasculated or has his male organ cut off shall enter the assembly of the LORD.
The Early Church Fathers say:
The Letter of Barnabas
“Moreover, he [Moses] has rightly detested the weasel [Lev. 11:29]. For he means, ‘Thou shall not be like to those whom we hear of as committing wickedness with the mouth with the body through uncleanness [orally consummated sex]; nor shall thou be joined to those impure women who commit iniquity with the mouth with the body through uncleanness’” (Letter of Barnabas 10:8 [A.D. 74]).
**
Clement of Alexandria**
“Because of its divine institution for the propagation of man, the seed is not to be vainly ejaculated, nor is it to be damaged, nor is it to be wasted” (The Instructor of Children 2:10:91:2 [A.D. 191]).
“To have coitus other than to procreate children is to do injury to nature” (ibid., 2:10:95:3).
Hippolytus
“[Christian women with male concubines], on account of their prominent ancestry and great property, the so-called faithful want no children from slaves or lowborn commoners, [so] they use drugs of sterility or bind themselves tightly in order to expel a fetus which has already been engendered” (Refutation of All Heresies 9:12 [A.D. 225]).
The Dictionary says:
Online Etymology Dictionary - Cite This Source
**adultery **
“
voluntary violation of the marriage bed,” c.1300, avoutrie, from
O.Fr. avoutrie, aoulterie, noun of condition from avoutre/aoutre, from L. adulterare “**to corrupt” **(see adulteration). Modern spelling, with the re-inserted -d-, is from c.1415 (see ad-). Classified as single adultery (with an unmarried person) and double adultery (with a married person). O.E. word was æwbryce “breach of law(ful marriage).”
The Catechism of the Catholic Church says:
**IV. OFFENSES AGAINST THE DIGNITY OF MARRIAGE
Adultery **
2380 Adultery refers to marital infidelity. When two partners, of whom at least one is married to another party, have sexual relations - even transient ones - they commit adultery. Christ condemns even adultery of mere desire.170 The sixth commandment and the New Testament forbid adultery absolutely.171 The prophets denounce the gravity of adultery; they see it as an image of the sin of idolatry.172
2381 Adultery is an injustice. He who commits adultery fails in his commitment. He does injury to the sign of the covenant which the marriage bond is, transgresses the rights of the other spouse, and undermines the institution of marriage by breaking the contract on which it is based. He compromises the good of human generation and the welfare of children who need their parents’ stable union.
When we have sex alone we are cheating on our spouse.
The Sixth Commandment says:
vatican.va/archive/catechism/p3s2c2a6.htm
scripturecatholic.com/contraception.html