I'll keep this brief.
Relationships are not about you fulfilling selfish desires. They are about working together to be better than when you are alone. This means you will have to change. This means it will be hard.
If you enter into a relationship with the wrong motivation it will be a wreck in no time at all.
I'll put it this way: It takes commitment to really love someone.
Happy feelings, sexual desire, etc are all part of a successful relationship but if you are not prepared to commit above all else, through thick and thin, in sickness and in health (especially when you don't feel those nice things for your partner) then you are not a real man.
I could also have titled this piece "Grow up and commit" because it is much the same thing.