If you like what you have, why look for what you don't?
Once, I dated a guy we'll call Peter. Peter was tall. Peter was dark. Peter was handsome, and more than that, Peter was kind. We saw each other pretty regularly, about three or four times a week, and not only was he nice but he was good in bed.
I enjoyed his company. We should have started officially dating. But I couldn't do it. I was madly, completely, and totally in lust with a guy named Lee, who worked at my law firm.
Lee was tall, slim, and as arrogrant as possible for a human being to be and still interact with the rest of the world. We'd had a one-night stand, and ever since, I couldn't get him out of my head.
He ignored me, other than to put in his morning Starbucks order. I didn't care. I couldn't commit to Peter. I made semi-lewd comments to Lee. I asked him what he was doing that night. I did everything short of strip when he asked for his quadruple espresso.
Eventually, Peter got sick of my lack of commitment, which he suspected was because of someone else. He stopped calling. Later, I heard he was seeing a redhead from another state.
I should have enjoyed what I had, instead of chasing what I didn't. Chasing doesn't have any guarantees. Neither does dreaming. Instead, you have what you have, and if that's something good, you ought to enjoy it instead of paying all your attention to someone else.
Otherwise, you risk losing what you already have. No one wants to hang around while a girl chases after some other guy. As soon as he finds out he's not number one in your life, he's probably going to dump you and go find someone who will make him number one in her life.
It's the old proverb: a bird in hand is worth two in the bush. I'd say a boy in hand is worth two in the bar. When you have a guy who's what you want in a person, you don't go chasing after someone else who just might have it more: more looks, more money, more fun. You keep hold of what you have.
Good guys are hard to find, and chances are, the guy you're chasing isn't one. If he was, he'd probably tell you gently to stay with what you've got.
In fact, we generally call what you're doing "attempting to cheat." Cheating is always reprehensible, especially when it's premeditated.
Why are you chasing this second guy, anyway? I was chasing Lee because I'd f*cked him once and wanted to do it again. I had no delusions of his kindness or our compatibility or some kind of longterm prospects. I was thinking with my lady parts. I simply missed the lay — it didn't have anything to do with Peter.
But a lot of the time, it does have something to do with the person you're currently seeing. Your relationship is missing something. Maybe it's missing good sex, or a certain kind of sex. Maybe you want a guy with better looks, or a nicer car, or someone who's kinder. If that's the case, you need to evaluate if it's worth it to stay with that person and stop chasing the one you want, or drop them and go fully after the other guy.
But mostly, it's better to enjoy what you have and stop chasing what you don't. You would only see a guy if he had what you wanted in the first place (that is, if you have any relationship sense, and if you don't, that's a whole other conversation).
What you're chasing probably isn't actually a guy. It's probably a dream of a guy, of a kind of life you've built up for yourself. And that's dangerous because even if you get it, it won't be what you want. So enjoy what you have, instead of chasing what you don't.