If it made me want to have sex with the person (I don’t mean marry and have marital relations), it would of itself be temptation, but entertaining it would be sinful.
As for natural attraction, it’s not sinful, so experiencing it is not sinful. Welcoming it may be a bit more problematic, but there’s some difference between attractive and sexy, isn’t there? I remember some time ago in a thread here I said something along the lines of intending and obtaining those sensations of attraction being wrong… A missaying on my part, confusing at best. I don’t remember which thread it was for sure, but anyway. It can’t really be sinful if I want to look at an attractive lady, so long as I don’t start entertaining thoughts of possessing her sexually, obtaining sexual gratification from it etc. But if I make the choice to go out with an attractive girl, I guess I also make the choice to experience attraction to her. In that sense, it doesn’t ring wrong to me.
If I start experiencing sexual temptations, I stop looking. If it’s sexually intended, I don’t look (sometimes comes with the fight if the model is particularly pretty and doesn’t look slutty - sluttiness creeps me off so much it defeats the purpose).
What troubles me recently is that Jesus said whoever looked upon a woman to lust after her, committed adultery with her in his heart. This suggests mortal sin and the fact that I can’t precisely tell the difference between normal attraction/appreciation and the disordered kind. I know the extremes - when it’s not a sin and when it’s definitely a sin, but I don’t exactly know at which point it becomes a sin. This is further complicated by the fact that sins against the VI are believed to be all grave matter by traditional moral theology. So sometimes I have a conflict between scrupples and reason when evaluating a situation in which I looked on purpose, the reason clearly being the lady or picture or sculpture or a rendered figure in computer graphics being attractive (it’s actually easier with real persons for some reason, maybe related with dignity), but then some form of temptation came and I didn’t know if I fought it well enough. Or the reaction became a bit stronger or a bit more biological and while I did stop looking, perhaps it took a fight. Then comes the problem of my having intentionally done what led to the temptation that came.
If 1) the intentional quality of looking, 2) the presence of at least minimally disordered desires or reactions made a mortal sin in a split second, the world would be full of mortal sin. But it is anyway and this is not exactly a proper argument. Knowledge and consent being less than full mitigate responsibility, but don’t ask me at which point it becomes or stops being mortal. I don’t know. It must be mortal if an informed person with uninhibited will chooses to engage in a sexual fantasy because it feels good. But, “looks to lust after,” doesn’t mention fantasies. It talks about just looking. I’m not sure if a single short somewhat charged and not really pure glance makes a mortal sin, but it looks quite serious to me. It somehow tends to feel to me that merely looking and then stopping when something starts feeling awry doesn’t make the sin completely avoided. I’m also not sure to what extent lust is possible without genital sensations - improper thoughts, disrespectful looks etc, but without a strong feeling coming “from there” - and if that can be mortal. In that case, it wouldn’t be, “I want some of that,” as much as, “I want an eyeful.”