I’m guessing that the reason you put up with all of this is that you still love your bf and you are concerned about what breaking up would mean for your little girl. Those are powerful reasons. But your story makes me very, very concerned for you – especially when you tell me that he is willing to let you and your child be hungry while he spends time with his lady friend.
All the signs point to your bf being more interested in being with the other woman than in making a family with you. You may be distracting yourself by thinking about whether you can trust him instead of confronting the very real and probably scary possibility that you may end up being a single parent, needing to take care of yourself and your daughter on your own.
Every day that goes by, your daughter is taking in the idea that what she observes in your relationship is the best she can she can expect from a partner someday. An important question to ask yourself is whether this is the role model you want her to have.
You were only 17 when you got together with your bf. It could be that you would choose differently now. But if you both want to make a go of it, I hope you can get him into couples therapy with you so he can learn how to be a faithful husband and loving father who provides for his family first. If he wants out, I hope you will give yourself the gift of seeing a therapist to help you build up your self-esteem. You deserve to have a partner who gives you (and your daughter) love and loyalty and who wants to be only with you.
I wish you well.