You knew your ex-boyfriend sold drugs when you were with him and it didn't matter, you stayed with him. You knew he sold drugs when you first got pregnant, and it didn't matter. Now all of a sudden, you've found out he cheated on you and he's such a bad person that you don't want him around your baby. I think your feelings have more to do with vengeance and getting back at your ex then it does with what's best for your baby.
It's completely normal for a teen father to freak out when being told he's about to become a father. He's a kid. Heck, you have 40-year old men freaking out and they're supposedly adults. And the first go to answer is to get rid of it. He's not carrying it and it's not his body so abortion seems to be an easy out. Right now you're only 4 months, barely showing, and it's still new for him. While you have hormones racing through your system ensuring you love your baby will all your heart, body, and soul, he doesn't. He's the same today as he was 4 months ago. So give him a little slack if he's not head over heels just yet.
Wait until your baby's born before you decide what to do. If he was really such an awful person, you wouldn't have been with him - at least I'm hoping you wouldn't have been with him. Once he has something concrete to hold and love, you'll be surprised at what he may or may not do.
Regardless, the teen years are for dating and finding out who you are and what you want out of life. Very rarely does a 17-year old end up with the person they're dating. It's just not what the teen years are for. So it's normal that ya'll broke up. Most teenagers do. It's normal to be pissed that he cheated on you. I would be too. But being a mom means you do what's best for your baby, not what you feel like doing at the moment and not based on your projections of what might happen in the future. A baby deserves the love of its mom and dad and you should do everything in your power to ensure your baby gets that.
PS Candida is simply yeast. It's no big deal. Yeast infections are common in pregnancy due to hormonal changes. In addition, they can be caused by changes in detergent, condoms, semen, non-cotton panties, etc. While men generally don't have symptoms, the fact that your boyfriend did is still no big deal.
PS If anyone on this board contacts you about giving your baby up for adoption or about adopting it themselves, report them. They're not good people.