Everyone is constantly searching for companion and
even if you are in a satisfied relationship and you long ceased the
search... people search for you instead. Sourcing and temptation is
part and parcel of having (not having) a relationship.
This is a constant.
Your question seemed to bend towards spiritual
aspect of Love, where you question about fate.
I sincerely believe that no one is destined to be alone. The word
'DESTINED' is a word not found in Western Astrology because we
believe in freewill. Hence I often substitute the word 'DESTINED'
to 'Tendency'. It was also commonly mention that if you manage to
change your fate - you are DESTINED to change it. So it is possible
to change your destiny and this word 'DESTINED' is actually a
negative attitude to perceive situation, for one often adopt a
passive and nonchalant way of handling
things.
In all my studies and humble opinion, chances are, you have yet to
grasp the full understanding of why you have landed in such plight.
Please note that we all have the POWER to change any aspects in our
life. This is so fringing` true - the human mind, heart and soul
TOGETHER can achieve things beyond your imagination. Trouble is,
most people don't know that they have the innate power to perform
all that. It was believed that 'only' certain people could have it.
To make things worst, we often do not know WHY it is like that and
HOW to go about doing it. Other people may have NO problem with it
because they discover a way/method that works for them and they
understand certain logics faster than you do.
But they are human like yourself. They are not deity and do not
possess supernatural powers. What they know... you have the ability to know
as well.
In simple: (1) There is something that they understand and you have
yet to... (2) something good that they possess and you have yet
to... or (3) something negative that you have acquired unknowingly
and it wasn't found on them.
I cite you one good example: When I talk to people
and probably share one Love theory from CloUdiSm, say, 'Love and Relationship is but two separate
entity. You can love someone, but it doesn't mean you have to be in
a relationship with him/her.'
Logically speaking, everyone understands this. But when you do a
little application here, there will be this distinct group of
people who don't understand, even logically speaking they
understood (You have to think deeper... slightly chim here, but I
hope you get the drift). For example, you talk to this guy who
showed all the signs and symptoms of a possessive man. He is likely
to be AWARE that possessiveness is a negative trait, but when
circumstances trigger the natural possessive nature in him, nothing
make sense to him.
This man tightened his claws because he felt that he is losing the
relationship. He never stop. In fact, he tightened his grip even
further as there are strong evidence that his woman is fleeing from
him. His grasp gets stronger and stronger.... until the
relationship snap forcefully. You can tell him ALL day that his
possessiveness is killing the relationship and he retorts by saying
'So what you mean? She is running
away from him and you expect me to release her by letting her do
what she wants and watch her leave me?'
At the end of the day, the man still loses his woman and STILL
doesn't understand anything. So I ask you people: who is at fault?
Fate or personality? Freewill or destined? You think this is an
impossible scenario? In fact, such cases are pretty common
enough.
When we talk about marriage - how many people getting married can
safely say that this marriage is the fruition of their Love?
Settling down in a marriage completely born out of freewill,
maturity and absolute clarity of what they want? In Singapore,
almost (30%), for every three marriages, one would end up in
divorce. Which goes to show that close to a third of these
marriages, which adds up to more than 6000 marriages, probably
doesn't know why the word 'marriage' in the first place and what
Love actually means to the 12,000 odd individuals. 
The truth is, most people
married to circumstances, not exactly fruition of
their Love, which is supposedly the ONLY reason why a marriage
should ever happen.
Even our biological clock shouldn't be the FIRST pull factor into a
marriage for real Love is spiritual - it transcend beyond emotional
and physical realm. It's isn't surprising to hear stories of couple
hastily getting into a marriage because they are not that 'young'
anymore and only to see them getting divorce some years down the
road because of incompatibility. 
***
There are reasons why some people don't get it and
why others seemed to have no problems in Love. The reason is
yourself. Your chips to success in Love depends on
how well you can absorb from your setbacks and to improve your
future until you come to a stage where you blend reality with
personal ideology principles. How well you handle your relationship
and to keep the passion alive depends largely on how well you
understand about your relationship, yourself, your Love and what is
workable for you.
Fate in Love?
The reason is
still yourself. 
Cheers