the idea of love bothers me, because you sort of throw rational thinking out the window, stop asking why something actually matters, and just decide that this significant other intrinsically matters to you.

Not at all. It's not that rational thinking goes out of the window, only your system of values changes.

You can stay perfectly rational, it's just that now "making that other person happy" is a huge value for you. A terminal value.

And you can ask yourself "why it matters" -- the answer is that you have a new terminal value and terminal values are where the "why" process stops.

How can you commit to something so permanently?

You can't. It's an illusion. But it's a useful and pleasant illusion :-)

there is probably a form of love that is rational to take.

You don't take love. Love takes you.