What a nasty man to do that to you, especially when you were pregnant!!
You may not believe it as you're feeling so down but you are doing so well. Going to college, getting a place at uni - you should be so proud of yourself.
When my H left me for OW, I was in bits but I signed up for college courses and started Pilates and it has helped so much, also with meeting new people. Although I love my friends dearly, it's actually nice to meet people who don't know the pain I've been through and see me for just me. When you start uni, can you get a babysitter now and again and arrange social events with your fellow students?
Bringing up a child on your own is very hard, I've done it, but the rewards are tenfold. You can do this lovely.
It sounds like you need some time for you, to find out exactly what you need to make you happy. It sounds like you're not ready for dates and just need a bit of pampering and time to discover who you are without this a.hole man in your life. He is tormenting you.
I too would suggest seeing your GP, mine has been so supportive. I understand the wanting to try hard for yourself but it's okay to admit you need a little bit of help.
You can do this, take lots of cuddles from your DD.