You can fall in love with anyone, anytime. Two people at once, three, as many as your heart wants. Just remember, if you love two people at once, choose the second one. Because if you really loved the first, you wouldn't have fallen for the second.
You can fall in love more than once with different people, but not at the same time. No one has control over falling in love, though you should know someone well enough to be able to fall in love with them.
As many times as your body wants but the real thing you need is self-control to either accept or ignore, now there are risks and all have rewards but we all know a reward can be bad or good, your choice...
You can fall in love with many people, then comes the part about self-control. You must be able to care for, or love someone without acting on it in a inappropriate way. I do not espouse the position so frequently quoted that if you loved the first person, you would not have fallen for the second one. That is just not true. If the second one has qualities that you love, maybe qualities the first person doesn't have in such abundance, you can love the second one too. Doesn't mean you don't love the first one. There's nothing that blocks your heart from loving another person just because you love one, what blocks it is your head; and the block might well be you do not act on it...does not invalidate the first love, get over that notion.