If you understand "love is love" then you'll understand that "love is love is love" is the same but more assertive. In English, repetition increases emphasis. For example:
He was a man among men, among men.
means, "He was very, very manly."
The meaning can vary with context. For example:
"Cake is cake", she said, "but I prefer pie."
means that she feels cake is nothing special. If instead she said, "Cake is cake is cake," it would only emphasize how uninterested she is in any kind of cake.
Sometimes this makes sense, sometimes it doesn't. It's one of those structures that works best when it's unexpected, and not overused.
Miranda's repetition of "love is love is love is love ..." emphatically implies the assertion that all people to love who they choose, in the way they choose, even though many (in the US) want to deny them this right. It helps if you fully understand the political context behind this statement, and why the situation makes him so emotional.
(Edit) The structure "X is X" is actually a kind of ellipsis, meaning that it's short for a longer sentence, expression, concept, or thought. The words are left out because they're obvious from context, or because (in this case) the expression version has more direct emotional impact.
For example, in the above example, "cake is cake" can be short for, "Cake is just the ordinary dessert 'cake' which I don't really care for."
The two of them are always fighting! I'll never understand how they stay a couple, but what can you do? Love is love.
Here "love is love" could be a short, simple version of the more complex thought:
'Love' is a combination of many weird and inexplicable attractions which we collectively group as a single word, 'love' but we don't really understand.
Again, the structure has no single meaning. You have to understand what the writer (or speaker) is trying to say. It should be obvious from context, but might sometimes require some understanding of current events.
With Miranda, you have to understand how the US is going through a painful political shift with this new Trump administration, which is leaving a lot of people feeling excluded or persecuted by religious fundamentalists who have been given a lot of power. It helps also to know about this event where after the show the stars of the very popular music "Hamilton" delivered a special message to (then) Vice-President-Elect Mike Pence, a very conservative Christian governor who has consistently voted against LGTQ rights, and who was in the audience that night.
So this version of "love is love is love is love etc." has a lot of subtext.