Relationships, why do they end?

It's been awhile since I have written anything.  I’ve been working/traveling a lot this past month and dealing with an old relationship.  This girl and I had a 3.5 year relationship that had it’s ups and downs because of trust issues and my potential in-laws and her daughter…..  ok – to clarify.  Her parents are total A-Holes and her daughter is a lying brat at age 17… she acts like a 9 year old.  Anyways…  We have been broken up 5 months now.  She had been sending me letters of her UNDYING love for me,  that she’s need me, that there was no one else, she will wait for me to figure things out, she knows that I am the ONE….bla bla bla.

Well, I had been listening to her and starting to think that maybe we could work it out and that the fact was I missed her too.

We would email mail a little and write to each other but 3 weeks ago I woke up in the middle of the night and just new she was with some one.  I am ashamed – but I went to her place and there was a car next to hers in her small apartment complex that I have never seen.  Could be nothing, right?  Besides … it wasn’t really any of my business.  But hears the deal… a good part of why we broke up was that I didn’t trust her – not only for cheating on me but for little things too.  Also I had a fear that if we got married she would leave me if things got tough.  So going on with the story....

Now I had to know what the deal was with this car.  She continued to give me poems and letters of one of a kind love and that she was there waiting for me.  I went to her place on Wednesday mornings and Friday mornings for 3 weeks (She doesn’t have her daughter on Tues/Thurs. nights.  Sure enough the car was there but never on the other days.  Just this Sunday she ask me to stop over because she wanted to give me some of her writings.  I stopped in and it was good to see her (I had seen her like once a week for some talks over the past 2 months).  Like I said these letters were very convincing and it was amazing to “think” someone felt this way about me.  Well I had to get closure of some kind.  I went to her apartment this morning and waited this time…. Sure enough a guy walked out of her door and got into his car and left.

I feel very betrayed, hurt, deceived, and disappointed.  I think that if someone is in love with the other person that much, then you don’t have someone staying over night spreading your legs for??