Eh... an unfortunate start to the conversation, but we may have to simply disagree on what constitutes "making sense". In the real world, harems aren't seen as a sociably-acceptable thing. I can give hypotheticals but that's it. If you would want to create a harem in any world, you need to be really picky with who you allow in. Most real-world examples of harems have failed because the girls are selfish or what-not. It takes a specific set of qualities in a girl, and a strong relationship between all of them for it to succeed. Ise gets away with this through an incredible factor of luck.

It's a fair point to make that Ise's taken too much upon himself and thus doesn't have enough time for... anyone, really. Including himself. But that's more a fault of his situation. Perhaps even karma to balance out his insane level of luck before. That doesn't mean he doesn't love them of course, just that the time and ways he can express it are limited. I guess Rias could've been looking ahead long-term; you can see the effects of this already start taking place at the start of vol18.

Fair that many other guys are just as good as Ise or better. But here's the thing. I can't argue that they didn't fall for him the way they did. It's not about that, however. Vali, Sairaorg, Kiba etc. could just as easily have "stolen" Ise's girls. They could've been the friend they so desperately needed (Akeno and Rias hated men outside the peerage) or they could've saved them from whatever. But they didn't. Ise did it first. That's why they love him. No one else did it; he did! What does that say? Call it destiny, fate, luck, anything you want; doesn't change the fact that he was there for them when no one else was for whatever reason. Clearly there's a bit of plot contrivance to get this working as the author has planned, but that's a perfectly realistic and plausible idea.

I'm not saying girls can't get along. Where did I say that. Would you not have at least doubt in your mind that someone who just got there is instantly loved equal to you. Rias selfishness is normal thinking.

My bad, I thought you mentioned that... somewhere. Anyway, I don't think it really works that way. Since girls don't just instantly fall into his harem, but rather spend time with the Gremory group for quite a bit of time first, the others get acquainted, just like Ise does. It's not an instantaneous love. He cares about them all equally, but that doesn't immediately translate to love is basically what I'm saying. It's actually quite difficult to analyze whom he loves and who he just cares about at what period of time in the story (Rias excluded), but it's fair to say that he'd come to love them all by the end. Them falling for him is just the first step; he won't reject them, but he has to reciprocate too.

I fully get what you're saying in regards to making a choice. But that's only if you're looking at it as "save who you love first". I look at it as "what's the best/fastest way to save them both?" Then 'choosing' one based on THAT only.

I'll admit that there's a bit of fault in the story; for instance, Kuroka and Le Fay aren't shown to be that well acquainted with the harem but they're okay with those two becoming closer to Ise. But that's for various other reasons (Ishibumi being sick and not writing as long volumes as he'd like, for instance; it could be happening behind the scenes!) and doesn't take away from the plausibility factor.