I believe I can help you with your concern
I am so sorry that you are having these difficulties with connecting with men, I can understand how that can distress you
May I ask you for how long have you thought that you may be bisexual or interested in women in a sexual way?
And before this attraction started were you still having trouble committing to a guy?
So it is possible that you have this anxiety when things get too serious with a guy because you are subconsciously afraid of being vulnerable and getting hurt, which is natural, or because you have always harbored subconscious attraction to females, but have not expressed it and that is what causes you anxiety, or it could be a combination of both.
Both instances are actually very common regarding your age, and it usually a normal part of life development.
I would encourage you to try a period of relationships with a woman to see if this eases your anxiety and if you feel more comfortable in a relationship.
You do not have to be sexual with a girl, but try going on a few dates to see if this i a path you are interested in. I think some of your anxiety is occurring because you are wondering about your sexual orientation and not sure if you should focus on men or women, and this causes confusion and anxiety.
And also for the afraid of commitment part, which again is natural, I would recommend some Cognitive Behavioral Therapy (CBT) techniques as this is the most evidence based therapy to treat anxiety. CBT has a premise that your symptoms are caused by negative thoughts, so if we change your thought process to be more positive and objective as well, then your symptoms will lessen.
Right now you focus on the negative thoughts which cause you anxiety and cause you to "back away" as you described it, so it would help to focus on an objective thought process to lessen that anxiety, so that when you do not want to be with a guy it will not be due to possible anxiety, but to your personal feelings.
So this link may help you, it contains a technique I use with patients called a thought record. It will help you keep track of any negative thoughts you have. You put the negative thought on paper, the emotion accompanying, the evidence to support it, and the evidence against it. Then I want you to come up with an alternative thought for the situation (more objective and plausible). This will help you change your way of thinking to be able to think more positive and not automatically go to a negative type of thinking.
In addition, these two worksheets are very good at helping lessen anxiety symptoms. It can help you focus on the big picture and the objective/positive thoughts and outcomes.
So I just wrote a lot, do you have any questions or concerns so far?
Anytime, I am always happy to help. Is there anything else I can assist you with today?
You are most welcome, I wish you the best regarding your anxiety and commitment issues. My goal is to provide you with excellent service, so if you ever have any further questions or concerns please do not hesitate to contact me at anytime. Before you sign off though, I would very much appreciate if you could rate my performance in helping you so that I can get credit for this question. Thank you very much