How can I remove my desire for a relationship/girlfriend? For at least half of my life I've had an extremely strong desire to be in a relationship/have a girlfriend and though I've tried, I've been unsuccessful and this has brought me tremendous suffering to the point where I almost committed suicide 2 years ago. I see couples in a similar age group as me every single day and this further increases my suffering. I first encountered Buddhism 2 years ago and through its teachings I've detached myself from the past and have removed my strong desire for material wealth and this indeed has removed a lot of suffering from my life, however, I just can't seem to let go of immense desire to have a girlfriend even after realizing that external circumstances never bring lasting happiness and fulfillment. 

How can I let go of this destructive desire?
What helped me tremendously distance myself is this:
Contemplate the various advantages and disadvantages of having a girlfriend--particularly the one that you think you would get--not the dream-woman-that-you-have-to-be-on-a-certain-level-you-are-not-at-to-get. 

For example, here is a personal list of benefits of celibacy:


Jing retention for transmutation into spiritual energy (chi, shen)
Time saved for spiritual and personal goals.
Money saved for spiritual and personal goals and fun.
Mental energy saved from all the headache and back and forth.
Social energy that can go into practical things like helping people or myself rather than feeding a woman's ego.
Less stress for managing a relationship... peace
Less stress about her cheating on me every day... peace


And disadvantages:


Lack of endorphins and excitement
Tactile loneliness
Social ignorance
Sexual ignorance
Intellectual ignorance about X


At this point you should have an overall idea if there is more advantage or disadvantage.

The last step is to FIND activities which address the disadvantages.


exercise
joining a sangha and doing social activities together
learning more more about female evolutionary psychology via videos/books (see Red Queen, Sperm Wars)
getting actual results of Buddha dharma


Lastly, I would say that it is best to pursue your path and not look for anything external because that external (i.e. girlfriend) when it comes to you "naturally" will be extremely well-matched for you (a great companion on your spiritual journey). Maybe it's because you started teaching or you were really successful and someone who values it took notice, etc.... let her find you.

Pursuing an un-ideal relationship would take you off the market and you might miss that girl of your dreams BECAUSE you were looking for her consciously and/or are with someone! Strange, isn't it? The best thing may be to be celibate until hotly pursued by someone well-matched. If it doesn't happen and you put all your 100% effort into the benefits list... then not much is lost!
But had you done the opposite... you will regret the sexual life for maybe eons or however long you think until you are a human and above with Buddhadharma.