While homosexual acts (along with other actions contrary to chastity, such as masturbation) are always wrong in themselves, the fact remains that a person's moral responsibility or guilt may be somewhat reduced by a lack of human freedom. Thus, we shoud take note of the difficulties created by ingrained habit and of the particular problem of psychological compulsion. Compulsion may be described as a narrowing of consciousness concerned either with a fascination for some object or with obedience to an impulse regarded as intolerable unless accepted (Rudolph Allers, "Irresistable Impulses: A Question of Moral Psychology," in Vol. 100, 1939, 208-219). In a broader sense, we may refer to compulsive behavior as that following the belief - born of past failures - that a particular urge is irresistible. Not many homosexual acts may be called compulsive when we consider the squalid circumstances (like a public lavatory) and the high risk in which they take place. But we must not assume that the compulsive person literally has no control over himself in the area of weakness. What happens, rather, is that the compulsive or strongly habituated person loses control (surrenders to an urge) under certain specific circumstances; and an analysis of the situation may help him (or her) recognize ways to exercise freedom in avoiding the circumstances which precipitate the compulsive or seemingly-compulsive action. In this effort the person needs prudent and often professional help - just as an alcoholic needs AA or another group or person that can help him avoid the people and situations that lead to a fall. In other words, if we suffer from a compulsion to some sinful activity, we are morally obliged to take what steps we can to prevent its activation and hence to overcome it.
In sexual compulsions the real problem is not the strength of the sexual instinct (which usually is not stronger than in normal individuals) but rather the inability of the individual to adjust to tensions within himself. To uncover these tensions, one needs the help of therapists. While under treatment, however, one must practice a rigorous honesty and avoid those things that may trigger the series of compulsive thoughts and events. With SSA, this often means actively avoiding homosexual haunts, movies, bars, baths, and pornography. It will also mean ending those relationships that one knows will lead to sin.
Significantly, examining the pattern of compulsive behavior reveals a very important feature: the impulses become irresistable before they have fully developed. As Rudolph Allers put it, "People have a presentiment of the impulse arising: they know that within a short time they will become entangled in a situation from which there is no escape, must as they desire one. They know that they are still capable, this very moment of turning away, and that by doing so they will avoid the danger - but they do not. There is a peculiar fascination, a lurid attraction in this kind of danger, and there is evidently some anticipation of the satisfaction that the partes inferiores animae [one's lower nature] will derive from indulging in the "irresistable attraction" (ibid., 216-217).
Thus, the "compulsive" (strongly habituated) homosexual will bear responsibility for his actions if he fails to resist temptations at the very beginning. To indulge oneself in any impure thoughts or actions is to play with fire: As one wit remarked, the trouble with irresistible impulses is that they are unresisted. It is no suprise that, thinking we are still in control, we find that we "unwillingly" get burned. In any case, despite any past or new sins, our responsibility is to resist temptation immediately each time it arises, gradually reducing the power of these impulses. To do this, one needs to find fresh motivation by following a plan of life such as I shall describe.
(Source: Same Sex Attraction: Catholic Teaching and Pastoral Practice by Fr. John F. Harvey, OSFS)