Yeah, I think you can, but it depends on the individual.
Some people, despite having the right feelings at heart, can just make stupid decisions. Maybe it's by buying into their own bullshit... maybe they think 'sex is just sex' or they're otherwise able to convince themselves that it's not a big deal and wont hurt anyone, etc.
I'm a little bit like that. Internally I can feel really devoted, yet still my mind can stray pretty easily. I guess I'm really not the most consistent individual on the planet, and am quite prone to the ebb and flow of various emotional states. One day I can be almost manically enthusiastic and optimistic, and the next day I'll find myself deep in some kind of depressive existential crisis, etc. Almost any sort of constancy can seem borderline uncharacteristic of me. This also seems to translate pretty well into any relationship (romantic or otherwise) that I have with other people.
My outlook on life can change at the drop of a hat, and I have a heart that tends to waiver all too often. I don't think it means I'm a bad person, or incapable of love... maybe just that my style of affection is kind of a rare taste... and that most people aren't likely to appreciate my flakyness. I just don't think I'm the most hard wired for the whole loving devotion thing, compared to some other people. Any sort of serious commitment (whether it be emotional or otherwise... ) can just have a way of making me go 'eek!'
I'm capable of devotion, but it's a lot of work and tends to run contrary to my instincts, and sometimes I just like to pretend that I'm the only one in the Universe who matters (ie: Sometimes I really want to disregard the potential my actions have to hurt others... perhaps because I'm feeling as if I'm slowly being imprisoned by the other person's expectations and feelings, and I just want to escape it all.) Even if sometimes that means running from the truth, burrying my head in the sand, or generally entangling myself in a web of my own bullshit, all out of some deluded sense of escapism in order to flee from responsibility...
I've made lots of stupid decisions just from those things alone: a load of responsibility, and the desire to escape it... and you can be quite sure I'll quite spectacularily fuck myself over or make my situation even worse, just by trying to wash my hands of it. It's kind of contradictory and stupid, but I'm used to expecting these sorts of things from me
I don't intend to hurt anyone, but of course that has little influence on the outcome.
And I've never actually cheated, but the thought often occurs to me. I don't even really consider myself the promiscuous type... but put me in the right set of circumstances, and I can see myself doing it. Don't get me wrong, I see cheating as a very serious betrayal of trust... but if asked to be entirely honest, it's not something I'm going to find unconscionable in every circumstance.
Sometimes I worry that trying to get a strong sense of devotion from me would be like trying to get blood from a stone... I care for people deeply, but it tends to be on my terms, and I am more prone to being somewhat aloof or non-expressive about it, and am really not the 'reliable' type (jeez, sounds like all the qualities classic of those who tend to take people for granted...) Basically, I'm not consciously a dick to those around me. If I hurt someone, it's usually just because I have a lot of weird (read: fucked up) interpersonal quirks... I'm the sort that tends to shoot myself in the foot more than anyone else I know.
Ironically, though, if a boyfriend gives me permission to sleep around, I
instantly lose interest in doing so... which makes me think it's kind of an escapist thing. When I can't do it, it can occupy my mind way more than I'm comfortable admitting... but once I get permission, suddenly I find myself not caring anymore! I think it's mostly the responsibility issue.
Give me lots of responsibility and I'll only want to flee. Treat me as if I have none, and I'll cling to you like a pest

But I am young and immature so I suppose that can also come with the territory.
I think some people are just a little silly, mentally, and will be prone to making some stupid decisions now and then. I know all too well the stupid decisions I can make. It's not as if there's some deeper, hidden agenda, or I secretly don't actually value people... my heart just tends to sway, and to get entangled in my own ridiculous bullshit way too often.