This is the definition of lust in the CCC:
2351 Lust is disordered desire for or inordinate enjoyment of sexual pleasure. Sexual pleasure is morally disordered when sought for itself, isolated from its procreative and unitive purposes. 
I find this definition vague, subjective, and unclear when I try to apply it to my situation.
I’m a Catholic, homosexual male. I instantly get aroused when I see a shirtless man, whether it’s a picture, on the street, or at the pool. I have the bad habit of looking at pics of shirtless men on the internet, especially on bodybuilding websites. Even when I go to the mall, there are pictures of shirtless men in clothing store windows and I can’t help looking at them and getting aroused. I see shirtless men on Youtube, on TV, and at the movies.
I’ve been confessing this sin over and over to the priest, and his advice is to give up the internet, keep your eyes away from any shirtless man you see on the street, and give up swimming at the community center. I ALWAYS fail to prevent myself from looking at shirtless men, because my thirst for this pleasure is too strong. I find the priest’s advice too impractical and extreme. He also told me I’ve committed sacrilege by receiving the Eucharist because of the sin of looking at shirtless men.
Is getting pleasure from looking at a shirtless man considered an offense against chastity? After all, it’s not porn or full nudity. Is it a mortal or venial sin? I haven’t masturbated in over 2 years, so this is just a mental problem. Also, I’ve NEVER looked at porn in my entire life. Women enjoy looking at shirtless men as well, so my situation is not any different from theirs. What do Catholic women do about this?