joanne, I can't endorse enough what the others have said. You need space and time to find yourself and find out the things which are important to YOU, and not to please someone else. Well done, and brave you, for making the split - you know it is the right thing to do, so start to have faith in yourself. You have made the big first step by admitting that you don't want to feel like this any longer.
Your dad dying has compounded the grief you feel - however hard the marital life, it's always sad when a relationship ends and you sound like you gave it your all. Your sadness for your dad will settle in time, you've had a lot happening all at once, so you need to allow yourself to live with that for a bit, and it sounds like you are now ready to start to move on.
Do a bit of self-assessment, make a list for yourself of what you are really good at, what you'd like to learn to be good at, and why people will like you when they know you - go out into the world and be who you want to be. You can't do much about "daddy's friend", just make your home a place where your little boy will want to come back to, and where he can make up his own mind - he must find it confusing too. A confident mum who feels happy with herself will make him feel confident about the situation.
"Small steps" is the way to do it. Step 1 you've done - step 2 - what about getting your hair done, go for something different? This is the New You!