why are some people in relationships unfaithful?

That is the problem. That is the problem. You need two people equally in love with each other. Getting sex is simple, I have been with a lot of people in friends with benefits and one night stand arrangements. But, to have someone to be in love with you at the same time you're in love with them and then keep that? It is very difficult.

I vastly prefer the bachelor's lifestyle of just having a lot of casual relationships, but, life happens. I am human after all and recently i fell in love with a girl i am seeing; and despite the fact i am usually so cold i could not help it at all. I really would prefer to not be in love.

I have no doubt that she is not as in love as i am, but i accept that i do not want to lose her either so i just keep seeing her for sex and love even though my instinct tells me that she is not in love with me. In my view, the love is not worth it, because the pain of losing someone is way worse than the emotional high you get from those amazing moments together. And the problem is, those moments you tend to remember for the rest of your life regardless of how badly things may turn out.

The terrible thing I have found with love and relationships is that you have to trust the partner to be in love with you also. Otherwise, it is a lie (people can and do pretend to love), and it tends to be a disaster waiting to happen. Because, if they fall in love with someone else (or they go with someone else with a ons or a fling) then it really usually means that your relationship is finito.

The problem is that we are human, can't beat ourselves up about it, it is just something we are blessed and cursed with. Pain and ecstasy are really weirdly linked.