I have a girlfriend who I like very much however, she seems not to have any feelings for me at all. I have tried to give her everything she wants and I know she enjoys having sex but only with her other guy buddies but never with me. She even chooses to have it with strangers and not me. Is it possible for a couple in a relationship to not have any chemistry at all

I was like you are now.

I went to see a therapist because of it.

The most important advice he gave me I will now give to you:

If you want gals to be standing in line for you, get out of the line you're standing in for them.

I will also give you the most important warning:

Be careful what you wish for, because you might just get it.

I hope you succeed.

You just know a girl who is taking advantage of you.

AMEN!

The fact that she is maintaining this fiction of being your girlfriend while blatantly screwing strangers demonstrates that YOU ARE HER DOORMAT.

Dump her. Dump her now. And most importantly because I already know what a sucker you are, dump her PERMANENTLY.

Gawd man, what is wrong with you that you'd put up with this?

You need to do some soul searching before dealing with women because you are wearing a great big neon sign that says "Lamb." And guess what? Women who are wolves are gonna shear you until there's nothing left.

Dump her irrevocably and get some therapy.

If she is not desiring a complete relationship with you now...  what would it be like in a marriage?   Successful love must be reciprocated.  
My ex-w was like this...  I was considerably poorer when I finally bailed.   I'd have been many thousands richer if I'd used providers instead of giving the ex everything, not getting sex...  

Go find someone who loves you for who you are.  Completely.  
skb

She treated you like a BUD (back-up dick) and you are always her f*cking BUD regardless. Get out now.
I was in the same situation and it was not just easy to walk away. Now I am very happy as she was completely out of my life and I am in a much better situation financially, sexually and mentally.
Good luck.

I enjoy giving advice to people in this situation.   Whenever you are loosing yourself in a relationship with a woman, you need to find someplace where there are other women that you can meet and talk to.  Whether in dating or in marriage, women will try to bring down your confidence so that they can get away with what they want.  Once you understand the game, you can never lose.    Since you have discovered the TER, you should do a little research and find a good provider who will show you a fun time and get your confidence back up. The key is to understand that other women want you and your "girlfriend" knows that too.  She just does not want you to figure it out.  Good luck.