I dunno.
In my experience as a guy who knows exactly what you're talking about, people will usually answer telling you to 'be yourself' or magically 'gain confidence' or even go so far as to suggest that 'weight isn't an issue'. Be assured that these sorts of people probably have no fucking clue what you've been through and aren't qualified to give you good advice.
Confidence is like this mythical quality that some people seem to be hoarding away and storing until winter for hibernation and other don't know where to look. In reality, gaining confidence comes from learning to accept and like yourself. What you can try, is to note that things that your good at, like you're preparing for a job interview. List the qualities that you like about yourself, that you wouldn't change for the world, that mean that you couldn't imagine being someone else.
Then you need to face the issues that you have with yourself and try to categorize them into things that you can and can't change. And then try to tackle the things that you don't like about yourself starting low down on the scale. Say for instance, you don't like that you stay up too late or that you drink/smoke a bit too much. Try making a concerted effort to make a change to your approach, very slowly and gradually but assuredly. I always find that working things into an automatic routine works well for this.
Try to get something to the point where it's automatic. Set yourself parameters, maybe (for instance tell yourself that you're going to walk 20 minutes extra a day, or drop those packets of potato chips from the diet from 2 to 1 a day, whatever). Understand also, that you may deviate from the routine from time to time due to unavoidable circumstances, a bit of over-indulgence. That's fine, just try to compensate for it and get straight back into your routine as quickly as you can.
Once you have one point down to being all but automatic, add something a bit more. Cut out the chips altogether, or go for a run round the block each day instead. Step it up gradually.
Here's where the magic happens. Whilst this is happening, you'll begin to become impressed with your resolve if you can sustain your efforts over a period of time. You'll be surprised with achieving what you didn't think you could achieve previously and therein lies the source of the confidence. It'll help you to feel good about yourself mentally whilst at the same time you'll feel better physically. You'll be alleviating two sources or angst at the same time. Now you're healthier in all regards and better equipped to take on new challenges and new routines and tackle other, perhaps bigger, problems.
The whole thing is cyclical and the starting off and keeping things as a routine is the hardest part. Of course, there is a tendency to relapse also a further period in, like a dietary mid-life crisis. Don't lose your shit if you feel like your rate of progress is slowing down or if you hit a hitch somewhere along the way. Try to get back into routine and understand that you are human and far from infallible. This is the stage that has knocked me off a couple of times. To remedy yourself, just tell yourself that you're going to work twice as hard to get back on track and know that you can from experience.
Now that's the weight/bad tendencies/personal peeves. The women. On this subject, I am definitely no expert but as far as I'm concerned, the key to being successful in that game is just changing your perceptions with regards to how you view women or potential partners. Try to understand that men and women are less different than everybody wants to make out and that at our very core what both genders want is to appreciate the emotion of caring for someone and also to be cared for. It's amongst the most basic of human instincts and needs.
Also, another advantage about being your age and lady-hunting is that the perceived maturity gap of the sexes is slowly negated as you grow older. Also, if immature partners was ever an issue, that's almost a non-factor. You are much more likely to be valued for your unbarbed humour and interesting conversation than any other superficial nonsense like dress sense and mannerisms and the like. Not that I said more likely, and not solely. Once you have come to appreciate and value yourself, you value in your opinions and abilities in these regards will grow also. What you have to say has plenty of worth, as it does with anyone and if you regard it so, so it'll come across to anyone speaking to you. This is why confidence is a well-perceived aphrodisiac; if you can convince yourself that you are a worthy partner, it becomes a great deal easier to convince others also.
As that's mostly it. It's a process best undertaken very slowly. Don't expect the heavens to open and the 'love yourself' thunderbolt to imbue you with magical powers. A longer and more gradual change is usually one more likely to last also. And don't pretend that you should always be perfect, you want to try to come to accept that many of your faults are what define you as a person and aren't worth trying to change. Start the ball rolling and before you know it, if you have some faith in your capacity for change, you'll be very surprised by how well your faith in yourself will reward you.