IslamWeb explains that the marriage between a Muslim woman and a non-Muslim man is Islamically invalid:
If he refuses to embrace Islam and remains a non-Muslim, then you should know that your marriage to him has become invalid from the day that you embraced Islam. If he did not convert to Islam within your 'Iddah (waiting period after divorce), then it is impermissible for you to remain with him. Rather, you must leave him.
Converting to Islam 8 months ago also means your iddah would be finished.
However, there are practical complications of being legally married to one man and Islamically married to another man, such as anti-bigamy laws and matters of inheritance.
Also note that "Muslim boyfriend" refers to a kind of relationship that's not appropriate in Islam (Dar Al-Ifta).