I’m 30 years old. I am in my second marriage and I have had several other relationships. They all start the same way, a strong desire to be close and exciting sex. After a few months, the desire for sex starts to wane. After a year I desire sex maybe once a week and it goes down from there. My first marriage ended after 5 years because my wife had an affair. I can't say I blame her much. I don't want my second one to go the same way. We have been married for 2 years now, and I am having trouble maintaining once a week sex. She is very sexual and would like much more. I have also been on the pill for 13 years and I have recently (3 months ago) started taking St. Johns Wort for minor depression. I have no trouble achieving orgasm once I am aroused.
How can I increase my sexual desire? Could being on the pill have an effect?

The only think i can answer truthfully here is the first lines. You had the strong desire, closeness and excitement, sexually at the beginning of each relationship but from there..... I don't know about pills etc that may be best for you to seek a professional answer.

But, if you were sexual at the beginning of each relationship/marriage then you enjoy that intimacy. You also state that you have no trouble achieving orgasm once aroused.

You may feel because the first marriage failed this one will, not at all, each situation is different so if there is any negativity there, you should get rid of it.

If your wife is sexual, then start giving more to her orally, and kissing her, i am sure that this will set you of. Think of each beginning of those relationships and what went on and re-visit it...

Also, ask her to fondle you more, touch you, etc.

It is obvious you can get aroused but just don't feel like it so reverse it and be in a position where you are going to get aroused so you do feel like it, as aposed to not being in that position and "play again".....

CW