Today's advice was requested by a man from the U.S. who we'll refer to henceforth as V. V asks:
"I have one girlfriend of 4 months who I've been drawing away from lately because of a new girl who I met in class. I'm going to let her know I'm single even though I'm not and ask her out in a few days. If she says yes, I'm going to stay with her. I thought about having 2 girlfriends in different social circles but I know something would go wrong.
I don't want to outright dump the 1st because I don't think she could handle it. She was devastated when I even brought up the possibility a month back and it took the whole night to get her to stop crying. I figured just saying I need a break and not bringing up the other girl would be easier for her, then maybe I could flip flop between the two. Turn it into a more casual but still closed, short term dating.
I'm going to study abroad next year with new girl and my current girlfriend still lives at home. So at that point breaking up with her is a given. I gotta loosen up the bond between us sooner than later either way. I don't want to hurt her because I do still care about her but saying I love you back when I don't mean it feels terrible.
Break up with your current girlfriend properly before asking out a second. You don't have to mention your lessening feelings for her or even the other girl, if you don't think she can handle it. Simply, "Our lives aren't headed in the same direction," would suffice. As that seems, more or less, to be the truth of it. Especially considering you've brought up breaking up in the past. Before this other girl was even in the picture.
She lives at home still, so now is a good time to do it as she'll have the support she inevitably needs to get her over it. You may also want to be a man and send one of her friends over to her house after you leave to stay with her. Just in case she doesn't have a stellar relationship with her parents/siblings.
Seeing both simultaneously is a recipe for disaster, and, makes you look like an asshole. Something you'll want to avoid if you plan on having a serious relationship with either of them, ever. Your current girlfriend can forgive you for breaking up with her. She will not however be likely to forgive you for cheating on her.
If the new girl finds out that she's essentially the other woman, that won't go over well either. You may think that'd she'd find your choosing her over the other girl to be flattering, but what it really does is show what caliber of person you are. In short, if you cheated on your ex she'll think you're just as likely to cheat on her someday too. And she's probably right.
You need to be confident enough to make a decision and follow it through like a man. Flip-flopping between both girls is flaky and can only ever end badly for all three involved.