I feel guilty for breaking up with my first girlfriend

I've started to feel guilty about certain things in my life and one of them is how I treated my first serious girlfriend. I thought it may be a good idea to try and contact her through social media, but when I did, she blocked me straight away. I just want to say sorry to her and let her know that I'm a different person from who I was.
I am 29 and happily married with a new baby boy. I don’t know why, but I had a dream the other day of my ex-girlfriend and now feel guilty about the past. I wasn't a very nice person back then, as my dad had died and it hit me very hard. I ended up pushing everyone I knew away from me, but mostly my ex-girlfriend. I really wished we had talked things through, rather than ending the relationship by text. It was ten years ago, but I can’t stop feeling guilty. Please help.
'Marks response'
What's going on in your life now that has brought these old memories and feelings up to the surface? How are you treating your wife and new baby? How does it feel being a dad yourself, has it made you think about becoming a better person and how you may have treated people in your life? Or could it be, you're unhappy with your life now and because of this you're starting to wonder back to old thoughts of when you were younger; the 'What if, why, when, or how?'. If you had done certain things a different way, you may have taken a different path in life.
It doesn't really matter what the answers to these questions are, or if you're really happy with your life, at this moment in time. All you need to realise is, that the choices you made in the past are all part of the future and here and now. And for you, the here and now is what you have. Feeling guilty about situations you put yourself and others through, won't make any difference to the here and now. All it will do is take your focus away, from the light in the future and keep you looking into the dark past.
Unfortunately, knowing this still doesn't change the fact that guilt eventually affects us all and will rear its ugly head at some point in our lives. I still feel guilty for things that I did 20 years ago: I can be standing in a queue waiting for my turn on the teacups or simply be tapping away on the laptop when all of a sudden a memory will pop into my head. It can be of anything or from any time in my life, but it will be something I feel guilty about doing.
If I let it, the thought can start to take me down the rabbit hole and all little burrows of it, deep into my mind. 'What if, why, when, how?' are all questions with endless answers that really are all unnecessary to ask. This is because you're not who you were 10 seconds ago, let alone ten years and if she doesn't already know this, then she's still who she was ten years ago, and that's a person you don't know or don't really want to know now.
You see, if you're willing to punish yourself for things you did in your past, then you're punishing an innocent man. What matters is that you're able to reflect on these things and know that you wouldn't do the same things now. Forget about this ex-girlfriend or how you left things. Move on with your future and bring your son up, to not necessarily make the same choices you did.