You are only suffering from an infatuation, a crush. It's not a
disease or madness, only something normal with all human beings.
Everyone at some point in time developes infatuation with
another, either with real life figures or fantasy
figures.
But gradually, over time, when we realize the futility of it,
when we do not get the responses we crave for from them, we grow
out of it and seek for someone more real whom we can love and who
loves us.
However, should you continue to build your world around this
person of your infatuation, feeding it with your imagination and
fantazies, and do not snap out it, it will become your reality,
which is a delusion, harming your mental health and missing out on
what you could have achieve in reality with similar effort and time
with someone else.
Love is born out of needs. It is very obvious that the person of
your infatuation has already found a man of her own that meet her
needs and provide her with love, comfort and solace. No other
person should rightfully come in between them and destroy something
beautiful that had blossom between her and her partner.
Not all relationships go smoothly, and has its up and downs,
which is only a purpose to know each other better - strength
weaknesses and bonds. And it should not be anyone else biz to take
opportunities when their relationship is down, when they are both
at their most vulnerable, to separate them for one's selfish
needs.
It is a despicable act and hated by almost everyone, an
ungentlemanly act, no honour involved, but sadly, something some
modern people seldom bother anymore....and term such acts as 'all's
fair in the game of love'. But love is not a game...
I am in no position to give advice, but I suggest that you leave
the couple alone. Give them your blessings instead and wish them
well, give them encouragement when they hit rock bottom with the
courage to stand up again with compromises for a long and lasting
future together.
As long as you are sincere and genuine, you will always find
friends, and within that circle friends whom will get to know you
well and you them, love will blossom for you just as it had for the
person of your infatuation. In time, your crush will ebb, with you
spending more time and effort to build up your world around the one
who loves you and whom you will love, cherish and treasure.
Good luck.