do things really happen without a reason?

Unexplained. Perplexing.
Sometimes I really don't understand the way things turn out.

Two of my good friends became very much closer after a trip. I just found out they have became a couple. The problem is both of them are girls.

Why oh why? I'm quite disturbed by it.
Both of them had been involved in normal boy-girl relationships before. One of them just broke up with her boyfriend less a year.

How did I find out? I did notice that they became much closer during the trip, but purely as friends. Until when we were working together on National Day, their actions made me suspicious. The lovey dovey look in their eyes. The secret smiles they had when their eyes met each others'. The lying on each others' shoulders whenever they had the chance to. The intimate close up photo nicely framed on her desktop.
Someone went to ask one of them and confirmed the fact.

So? That someone kept telling me that some things just happen without a reason. Somehow I'm really very reluctant to accept this explanation. I couldn't imagine myself becoming like them one day. It's not that I don't accept lebanism but I just can't justify their actions and thoughts at all. Both of them came from mixed schools and I really don't think they were hurt so deeply by their previous relationships that made them detest guys. Even if I'm desperate for guys(yes, I admit it) and get rejected by all the stupid guys, I don't think I will turn to like girls at all.

Unexplained number two.
I know a couple who have been together for 8 years. Months ago I still asked the guy when will he marry her. He told me seriously "3 years later when I have money". They broke up two weeks ago.

I was very shocked when I heard the news from the guy. He's like a brother to me. It was the girl that suggested the breakup. Reason was she felt that things were just not the same as before. All the while I thought they were happy and lucky couple. I know the guy really loved her and very much wanted to make her his wife.

Why oh why? I don't understand why. How can one believe in love when things just happen without a reason?