I have a deep fear of commitment...

I am a 25-year old guy and have been having problems with commitment. I have been in three relationships, but they have all lasted less than a year. I get close to someone but, whenever they start to get too serious, I back off and start to lose interest. I know this is unfair and probably childish, and I keep telling myself that the next relationship will be stable, but it starts to happen all over again. I am now so afraid of this that I don’t even go on dates because it seems futile. What can I do to get over this fear? Is there something wrong with me and should I speak to a professional counsellor?
A fear of commitment doesn’t mean there is anything wrong with you. it simply means that you are struggling with what is an extremely common problem that affects most of us at some point or another. Speaking to a professional will always help you gain more clarity, of course, but the important thing to do until then is stop putting so much pressure on yourself. Relationships need time to evolve and thrive.  They can’t be time-bound or managed by a manual. You can’t get into one with the assumption that one is going to be serious or not, because these are individuals with different personalities and expectations. Try and take things one day at a time, enjoy being in the present, and you may be surprised at how things change as you get older.

How can I convince my girlfriend to change some habits without coming across as being too pushy?
That depends on what these habits are, how she perceives them, and why you intend for her to change them. There is nothing that can’t be accomplished with communication, and not coming across as pushy simply depends upon how well you can explain to her why you want some things to change. Ask yourself why this is important first.