Expectant girlfriend is HIV positive

I am a man aged 26. I have been dating this woman aged 31 for about one and a half years. She is pregnant and during one of the antenatal clinics we got tested for HIV and unfortunately she tested positive.

Although I tested negative, I am afraid she may have infected me. She later told me that she had been living with the virus for the last five years. I really love her and was planning to marry her but I am now confused. I do not understand why she chose to get intimate with me when she clearly knew her status. Should I proceed with the relationship and plans to marry her? Please advice.